drm/i915/guc/slpc: Add selftest for slpc tile-tile interaction

Run a workload on tiles simultaneously by requesting for RP0 frequency.
Pcode can however limit the frequency being granted due to throttling
reasons. This test checks if there is any throttling but does not fail
if RP0 is not granted due to throttle reasons

v2: Fix build error
v3: Use IS_ERR_OR_NULL to check worker
    Addressed cosmetic review comments (Tvrtko)
v4: do not skip test on media engines if gt type is GT_MEDIA.
    Use correct PERF_LIMIT_REASONS register for MTL (Vinay)

Signed-off-by: Riana Tauro <riana.tauro@intel.com>
Reviewed-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221109112541.275021-2-riana.tauro@intel.com