R600/SI: Teach SIFoldOperands to split 64-bit constants when folding

R600/SI: Teach SIFoldOperands to split 64-bit constants when folding

This allows folding of sequences like:

s[0:1] = s_mov_b64 4
v_add_i32 v0, s0, v0
v_addc_u32 v1, s1, v1

into

v_add_i32 v0, 4, v0
v_add_i32 v1, 0, v1

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225369 91177308-0d34-0410-b5e6-96231b3b80d8