mei: pxp: add command streamer API to the PXP driver

The discrete graphics card with GSC firmware
using command streamer API hence it requires to enhance
pxp module with the new gsc_command() handler.

The handler is implemented via mei_pxp_gsc_command() which is
just a thin wrapper around mei_cldev_send_gsc_command()

Signed-off-by: Vitaly Lubart <vitaly.lubart@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220928004145.745803-6-daniele.ceraolospurio@intel.com