drm/i915/xehp: Xe_HP forcewake support

Implement Xe_HP forcewake handling.  While we're at it, let's reorder to
the forcewake assignment if/else ladder to match our usual driver
conventions.

Co-authored-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Stuart Summers <stuart.summers@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210723174239.1551352-6-matthew.d.roper@intel.com