drm/i915/guc/slpc: Update boost sysfs hooks for SLPC

Add a helper to sort through the SLPC/RPS paths of get/set methods.
Boost frequency will be modified as long as it is within the constraints
of RP0 and if it is different from the existing one. We will set min
freq to boost only if there is at least one active waiter.

v2: Add num_boosts to guc_slpc_info and changes for worker function
v3: Review comments (Ashutosh)

Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211102012608.8609-4-vinay.belgaumkar@intel.com