[AMDGPU] Ensure there are enough registers for wave dispatch

Summary:
This fixes the number of SGPRs and VGPRs in the *_RSRC1 register to
allow for registers set up in wave dispatch, even if those registers are
not used in the shader.

Re-landed after noticing that the buildbot failure from 329808 seemed to
be unrelated.

Subscribers: arsenm, kzhuravl, wdng, nhaehnle, yaxunl, dstuttard, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D45503

Change-Id: I6575f0e0d2a528d1319d0b289f0ebe4510fa5771
llvm-svn: 329826