radeonsi: add support for an on-disk shader cache

radeonsi: add support for an on-disk shader cache

V2:
- when loading from disk cache also binary insert into memory cache.
- check that the binary loaded from disk is the correct size. If not
  delete the cache item and skip loading from cache.

V3:
- remove unrequired variable

Reviewed-by: Grigori Goronzy <greg@chown.ath.cx>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>