rs6000: Add execution tests for mma builtins [v4]

rs6000: Add execution tests for mma builtins [v4]

This patch adds execution tests that use the MMA builtins and
check for the right answer, and new tests that checks whether
__builtin_cpu_supports and __builtin_cpu_is return sane
answers for power10.

2020-06-30  Rajalakshmi Srinivasaraghavan  <rajis@linux.vnet.ibm.com>
	    Aaron Sawdey  <acsawdey@linux.ibm.com>

gcc/testsuite/
	* gcc.target/powerpc/p10-identify.c: New file.
	* gcc.target/powerpc/p10-arch31.c: New file.
	* gcc.target/powerpc/mma-single-test.c: New file.
	* gcc.target/powerpc/mma-double-test.c: New file.