drm/xe/gsc: Query GSC compatibility version

The version is obtained via a dedicated MKHI GSC HECI command.
The compatibility version is what we want to match against for the GSC,
so we need to call the FW version checker after obtaining the version.

Since this is the first time we send a GSC HECI command via the GSCCS,
this patch also introduces common infrastructure to send such commands
to the GSC. Communication with the GSC FW is done via input/output
buffers, whose addresses are provided via a GSCCS command. The buffers
contain a generic header and a client-specific packet (e.g. PXP, HDCP);
the clients don't care about the header format and/or the GSCCS command
in the batch, they only care about their client-specific header. This
patch therefore introduces helpers that allow the callers to
automatically fill in the input header, submit the GSCCS job and decode
the output header, to make it so that the caller only needs to worry about
their client-specific input and output messages.

v3: squash of 2 separate patches ahead of merge, so that the common
functions and their first user are added at the same time

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.Com> #v1
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>