drm/i915: Rename pre-icl SAGV enable/disable functions

drm/i915: Rename pre-icl SAGV enable/disable functions

Give the pre-icl SAGV control functions a skl_ prefix instead
of the intel_ prefix to make it a bit more clear that they
are not some kind of universal things that can be called on
any platform. Also make the functions void since we never
use the return value anyway.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220309164948.10671-6-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>