drm/i915/guc/slpc: Initial definitions for SLPC

Add macros to check for SLPC support. This feature is currently supported
for Gen12+ and enabled whenever GuC submission is enabled/selected.

Include templates for SLPC init/fini and enable.

v2: Move SLPC helper functions to intel_guc_slpc.c/.h. Define
basic template for SLPC structure in intel_guc_slpc_types.h.
Fix copyright (Michal W)

v3: Review comments (Michal W)

v4: Include supported/selected inside slpc struct (Michal W)

Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Signed-off-by: Sundaresan Sujaritha <sujaritha.sundaresan@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210730202119.23810-2-vinay.belgaumkar@intel.com