vc4: Dump the VPM read index in QIR disasm.
vc4: Dump the VPM read index in QIR disasm.

Since the VPM reads have to be in order, it's useful to see their indices
in the dump.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler