drm/i915/guc/slpc: Adding SLPC communication interfaces

drm/i915/guc/slpc: Adding SLPC communication interfaces

Add constants and params that are needed to configure SLPC.

v2: Add a new abi header for SLPC. Replace bitfields with
genmasks. Address other comments from Michal W.

v3: Add slpc H2G format in abi, other review commments (Michal W)

v4: Update status bits according to latest spec

v5: checkpatch()

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: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210730202119.23810-4-vinay.belgaumkar@intel.com