We notice two identical copies of the shadow register table and
following from that removal can also unify CHV and Gen9 write
mmio functions and macros into a single implementation.

v2: Name fwtable consistently and use HAS_FWTABLE. (Joonas Lahtinen)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>