intel/fs: Use the ATTR file for FS inputs

intel/fs: Use the ATTR file for FS inputs

This replaces the special magic opcodes which implicitly read inputs
with explicit use of the ATTR file.

v2 (Jason Ekstrand):
 - Break into multiple patches
 - Change the units of the FS ATTR to be in logical scalars

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