[AMDGPU] Use PredicateControl in MIMGBaseOpcode. NFC.

[rampitec]

Summary

This is infrastructural, will be needed for future work.
For some reason it was only used in MIMG_NoSampler, while
needed everywere we use MIMGBaseOpcode if we want to use
predicates.

[msearles]

LGTM

llvm/trunk/lib/Target/AMDGPU/MIMGInstructions.td

 def MIMGEncGfx10NSA : MIMGEncoding;
 
 def MIMGEncoding : GenericEnum {
   let FilterClass = "MIMGEncoding";
 }
 
 // Represent an ISA-level opcode, independent of the encoding and the
 // vdata/vaddr size.
-class MIMGBaseOpcode {
+class MIMGBaseOpcode : PredicateControl {
   MIMGBaseOpcode BaseOpcode = !cast<MIMGBaseOpcode>(NAME);
   bit Store = 0;
   bit Atomic = 0;
   bit AtomicX2 = 0; // (f)cmpswap
   bit Sampler = 0;
   bit Gather4 = 0;
   bits<8> NumExtraArgs = 0;
   bit Gradients = 0;
let VAddrDwords = 4 in {
       def _V4_nsa_gfx10 : MIMG_NoSampler_nsa_gfx10<op, asm, dst_rc, 4,
                                                    !if(enableDisasm, "AMDGPU", "")>;
     }
   }
 }
 
 multiclass MIMG_NoSampler <bits<8> op, string asm, bit has_d16, bit mip = 0,
                            bit isResInfo = 0> {
-  def "" : MIMGBaseOpcode, PredicateControl {
+  def "" : MIMGBaseOpcode {
     let Coordinates = !if(isResInfo, 0, 1);
     let LodOrClampOrMip = mip;
     let HasD16 = has_d16;
   }
 
   let BaseOpcode = !cast<MIMGBaseOpcode>(NAME),
       mayLoad = !if(isResInfo, 0, 1) in {
     let VDataDwords = 1 in