drm/i915/pxp: Define PXP component interface

This will be used for communication between the i915 driver and the mei
one. Defining it in a stand-alone patch to avoid circualr dependedencies
between the patches modifying the 2 drivers.

Split out from an original patch from  Huang, Sean Z

v2: rename the component struct (Rodrigo)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210924191452.1539378-2-alan.previn.teres.alexis@intel.com