rs6000: Disable -m[no-]direct-move (PR85293)

rs6000: Disable -m[no-]direct-move (PR85293)

The -mno-direct-move option causes a lot of problems, since it forces
us to be able to generate code for p8 and up with some crucial
instructions missing.  This patch removes the -m[no-]direct-move
options so that the user cannot put us into this unexpected situation
anymore.  Internally we still have all the same flags, and they are
automatically set based on -mcpu; getting rid of that is a lot more
work and will have to wait for GCC 9 (in some places the flag is used
to see if we are compiling for a p8 _at all_).

	PR target/85293
	* config/rs6000/rs6000.opt (mdirect-move): Make deprecated.
	* doc/invoke.texi (RS/6000 and PowerPC Options): Remove -mdirect-move
	and -mno-direct-move.

gcc/testsuite/
	PR target/85293
	* gcc.target/powerpc/pr80098-2.c: Remove -mdirect-move.  Remove the
	corresponding dg-error clause.
	* gcc.target/powerpc/pr80098-3.c: Ditto.
	* gcc.target/powerpc/pr80103-1.c: Delete.

From-SVN: r259386