drm/i915/guc/slpc: Allocate, initialize and release SLPC

Allocate data structures for SLPC and functions for
initializing on host side.

v2: Address review comments (Michal W)
v3: Remove unnecessary header includes (Michal W)
v4: Rebase
v5: Move allocation of shared data into slpc_init() (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: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210730202119.23810-5-vinay.belgaumkar@intel.com