[AArch64, ILP32] 5/6 Pad pointer-typed stack argument downward in ILP32.

gcc/

	* config/aarch64/aarch64.c (aarch64_pad_arg_upward): In big-endian,
	pad pointer-typed argument downward.

gcc/testsuite/

	* gcc.target/aarch64/test-ptr-arg-on-stack-1.c: New test.

From-SVN: r201168