R600/SI: fix VOPC encoding v2

Previously it only worked because of coincident.

v2: fix 64bit versions, use 0x80 (inline 0) instead of SGPR0
    for the unused SRC2

This is a candidate for the stable branch.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
llvm-svn: 175352