Prevent producing real strange tablegen code by using
proper register sizes, alignments and hierarchy.

Also cleanup the unused definitions and add some comments.

v2: add SGPR 512 bit registers, stop registers from wrapping around,
    fix SGPR alignment

This is a candidate for the mesa-stable branch.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
llvm-svn: 176098