R600/SI: Avoid generating S_MOVs with 64-bit immediates v2

SITargetLowering::analyzeImmediate() was converting the 64-bit values
to 32-bit and then checking if they were an inline immediate.  Some
of these conversions caused this check to succeed and produced
S_MOV instructions with 64-bit immediates, which are illegal.

v2:
  - Clean up logic

Reviewed-by: Christian König <christian.koenig@amd.com>
llvm-svn: 178927