drm/i915/guc: Improve GuC load error reporting

There are multiple ways in which the GuC load can fail. The driver was
reporting the status register as is, but not everyone can read the
matrix unfiltered. So add decoding of the common error cases.

Also, remove the comment about interrupt based load completion
checking being not recommended. The interrupt was removed from the GuC
firmware some time ago so it is no longer an option anyway. While at
it, also abort the timeout if a known error code is reported. No need
to keep waiting if the GuC has already given up the load.

v2: Fix mis-matched case and confusing 'success' variable (Daniele).

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230316220632.3312218-2-John.C.Harrison@Intel.com