This test will validate we can achieve actual frequency of RP0. Pcode
grants frequencies based on what GuC is requesting. However, thermal
throttling can limit what is being granted. Add a test to request for
max, but don't fail the test if RP0 is not granted due to throttle
reasons.

Also optimize the selftest by using a common run_test function to avoid
code duplication. Rename the "clamp" tests to vary_max_freq and
vary_min_freq.

v2: Fix compile warning
v3: Review comments (Ashutosh). Added a FIXME for the media RP0 case.
v4: Checkpatch (strict) fixes, remove FIXME and other comments (Ashutosh)

Fixes commit 8ee2c227 ("drm/i915/guc/slpc: Add SLPC selftest")

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/20220627230346.27720-1-vinay.belgaumkar@intel.com