drm/i915/guc/slpc: Sysfs hooks for SLPC

Update the get/set min/max freq hooks to work for
SLPC case as well. Consolidate helpers for requested/min/max
frequency get/set to intel_rps where the proper action can
be taken depending on whether SLPC is enabled.

v2: Add wrappers for getting rp0/1/n frequencies, update
softlimits in set min/max SLPC functions. Also check for
boundary conditions before setting them.

v3: Address review comments (Michal W)

v4: Add helper for host part of intel_rps_set_freq helpers (Michal W)

v5: checkpatch()

Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Acked-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Sujaritha Sundaresan <sujaritha.sundaresan@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210730202119.23810-13-vinay.belgaumkar@intel.com