R600/SI: Only create one instruction when spilling/restoring register v3

The register spiller assumes that only one new instruction is created
when spilling and restoring registers, so we need to emit pseudo
instructions for vector register spills and lower them after
register allocation.

v2:
  - Fix calculation of lane index
  - Extend VGPR liveness to end of program.

v3:
  - Use SIMM16 field of S_NOP to specify multiple NOPs.

https://bugs.freedesktop.org/show_bug.cgi?id=75005

llvm-svn: 207843