drm/xe/gsc: Add debugfs to print GSC info

This is useful for debug, in case something goes wrong with the GSC. The
info includes the version information and the current value of the HECI1
status registers.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Reviewed-by: Julia Filipchuk <julia.filipchuk@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240828215158.2743994-5-daniele.ceraolospurio@intel.com