[AMDGPU] Add VALU to V_INTERP Instructions

Wait states are not properly being inserted after buffer_store for v_interp instructions.

Add VALU to V_INTERP instructions so that the GCNHazardRecognizer can
check and insert the appropriate wait states when needed.

Differential Revision: https://reviews.llvm.org/D48772

Change-Id: Id540c9b074fc69b5c1de6b182276aa089c74aa64
llvm-svn: 336339