drm/i915/gt: Add media RP0/RPn to per-gt sysfs

Retrieve RP0 and RPn freq for media IP from PCODE and display in per-gt
sysfs. This patch adds the following files to gt/gtN sysfs:
* media_RP0_freq_mhz
* media_RPn_freq_mhz

v2: Fixed commit author (Rodrigo)
v3: Convert to new uncore interface for pcode functions
v4: Adapt to intel_pcode.* function rename
v5: #include "intel_pcode.h" in alphabetical order (Tvrtko)

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Dale B Stimson <dale.b.stimson@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/45e34127a79e808f6582db8afb77f2f728a446e6.1653484574.git.ashutosh.dixit@intel.com