rs6000: Remove -mpower10 option (PR95907)

rs6000: Remove -mpower10 option (PR95907)

The only way to enable or disable Power10 insns (ISA 3.1 insns) should
be via the -mcpu= switch.  This patch disables the -mpower10 options the
same way the -mdirect-move switch is neutered already.  That is not an
ideal way, but it works, it is not the first, and doing it properly is
more work, and will happen later.

2020-07-24  Segher Boessenkool  <segher@kernel.crashing.org>

	* config/rs6000/rs6000.opt: Delete -mpower10.

gcc/testsuite/
	* gcc.target/powerpc/pr95907.c: New.