drm/i915/pxp: enable PXP for integrated Gen12

Note that discrete cards can support PXP as well, but we haven't tested
on those yet so keeping it disabled for now.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@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/20210924191452.1539378-18-alan.previn.teres.alexis@intel.com