arm: Implement vceqq_p64, vceqz_p64 and vceqzq_p64 intrinsics

This patch adds implementations for vceqq_p64, vceqz_p64 and
vceqzq_p64 intrinsics.

vceqq_p64 uses the existing vceq_p64 after splitting the input vectors
into their high and low halves.

vceqz[q] simply call the vceq and vceqq with a second argument equal
to zero.

The added (executable) testcases make sure that the poly64x2_t
variants have results with one element of all zeroes (false) and the
other element with all bits set to one (true).

2021-01-15  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	PR target/71233
	* config/arm/arm_neon.h (vceqz_p64, vceqq_p64, vceqzq_p64): New.

	gcc/testsuite/
	PR target/71233
	* gcc.target/aarch64/advsimd-intrinsics/p64_p128.c: Add tests for
	vceqz_p64, vceqq_p64 and vceqzq_p64.
	* gcc.target/arm/simd/vceqz_p64.c: New test.
	* gcc.target/arm/simd/vceqzq_p64.c: New test.