mei: add support for graphics system controller (gsc) devices

GSC is a graphics system controller, based on CSE, it provides
a chassis controller for graphics discrete cards, as well as it
supports media protection on selected devices.

mei_gsc binds to a auxiliary devices exposed by Intel discrete
driver i915.

v2: fix error check in mei_gsc_probe
v3: update MODULE_LICENSE ("GPL" is preferred over "GPL v2" and they
    both map to GPL version 2)

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com> #v3
Link: https://patchwork.freedesktop.org/patch/msgid/20220419193314.526966-3-daniele.ceraolospurio@intel.com