R600: optimize the UDIVREM 64 algorithm

This is a squash of several optimization commits:
 - calculate DIV_Lo and DIV_Hi separately
 - use BFE_U32 if we are operating on 32bit values
 - use precomputed constants instead of shifting in UDVIREM
 - skip the first 32 iterations of udivrem

v2: Check whether BFE is supported before using it

Patch by: Jan Vesely

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
llvm-svn: 207589