drm/xe: Raise GT frequency before GuC/HuC load

Starting GT freq is usually RPn. Raising freq to RP0 will
help speed up GuC load times. As an example, this data was
collected on DG2-

GuC Load time @RPn ~ 41 ms
GuC Load time @RP0 ~ 11 ms

v2: Raise GT freq before hwconfig init. This will speed up
both HuC and GuC loads. Address review comments (Rodrigo).
Also add a small usleep after requesting frequency which gives
pcode some time to react.

v3: Address checkpatch issue

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>