drm/xe/gsc: Improve SW proxy error checking and logging

If an error occurs in the GSC<->CSME handshake, the GSC will send a
PROXY_END msg to the driver with the status set to an error code. We
currently don't check the status when receiving a PROXY_END message and
instead check the proxy initialization status in the FWSTS reg;
therefore, while still catching any initialization failures, we lose the
actual returned error code. This can be easily improved by checking the
status value and printing it to dmesg if it's an error.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241106002402.486700-1-daniele.ceraolospurio@intel.com