testsuite: Add new tests for DFP under aarch64/aapcs64

This patch copies all existing tests involving float/double/long
double types and replaces them with _Decimal32/_Decimal64/_Decimal128.
I thought it would be clearer/easier to maintain to do it this way
rather than adding tests for DFP types in the existing testcases,
except for func-ret-1.c and func-ret-3.c.

This makes sure all cases tested for traditional floating-point are
equally tested for decimal floating-point.

The patch also adds a test involving loading DFP values from memory.

2022-03-31  Christophe Lyon  <christophe.lyon@arm.com>

	gcc/testsuite/
	* gcc.target/aarch64/aapcs64/aapcs64.exp: Support new dfp*.c tests.
	* gcc.target/aarch64/aapcs64/func-ret-1.c: Add DFP tests.
	* gcc.target/aarch64/aapcs64/func-ret-3.c: Add DFP tests.
	* gcc.target/aarch64/aapcs64/type-def.h: Add DFP types.
	* gcc.target/aarch64/aapcs64/dfp-1.c: New test.
	* gcc.target/aarch64/aapcs64/ice_dfp_5.c: New test.
	* gcc.target/aarch64/aapcs64/test_align_dfp-1.c: New test.
	* gcc.target/aarch64/aapcs64/test_align_dfp-4.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_1.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_10.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_11.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_12.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_13.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_14.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_15.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_16.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_17.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_18.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_19.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_2.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_20.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_21.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_22.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_23.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_24.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_25.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_26.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_27.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_3.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_5.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_6.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_7.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_8.c: New test.
	* gcc.target/aarch64/aapcs64/test_dfp_9.c: New test.
	* gcc.target/aarch64/aapcs64/test_quad_double_dfp.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-1.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-10.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-11.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-12.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-13.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-14.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-16.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-2.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-3.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-4.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-5.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-6.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-8.c: New test.
	* gcc.target/aarch64/aapcs64/va_arg_dfp-9.c: New test.