intel/fs: Replace the CINTERP opcode with a simple MOV

intel/fs: Replace the CINTERP opcode with a simple MOV

The only reason it was it's own opcode was so that we could detect it
and adjust the source register based on the payload setup.  Now that
we're using the ATTR file for FS inputs, there's no point in having a
magic opcode for this.

v2 (Jason Ekstrand):
 - Break the bit which removes the CINTERP opcode into its own patch

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>