drm/i915/guc/slpc: Use non-blocking H2G for waitboost

SLPC min/max frequency updates require H2G calls. We are seeing
timeouts when GuC channel is backed up and it is unable to respond
in a timely fashion causing warnings and affecting CI.

This is seen when waitboosting happens during a stress test.
this patch updates the waitboost path to use a non-blocking
H2G call instead, which returns as soon as the message is
successfully transmitted.

v2: Use drm_notice to report any errors that might occur while
sending the waitboost H2G request (Tvrtko)
v3: Add drm_notice inside force_min_freq (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/20220623003225.23301-1-vinay.belgaumkar@intel.com