drm/i915/pmu: Use functions common with sysfs to read actual freq

Expose intel_rps_read_actual_frequency_fw to read the actual freq without
taking forcewake for use by PMU. The code is refactored to use a common set
of functions across sysfs and PMU. Using common functions with sysfs in PMU
solves the issues of missing support for MTL and missing support for older
generations (prior to Gen6). It also future proofs the PMU where sometimes
code has been updated for sysfs and PMU has been missed.

v2: Remove runtime_pm_if_in_use from read_actual_frequency_fw (Tvrtko)

v3: (Tvrtko)
 - Remove goto in __read_cagf
 - Unexport intel_rps_get_cagf and intel_rps_read_punit_req

Fixes: 22009b6d

 ("drm/i915/mtl: Modify CAGF functions for MTL")
Link: https://gitlab.freedesktop.org/drm/intel/-/issues/8280
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230316004800.2539753-1-ashutosh.dixit@intel.com