drm/i915: Make intel_{enable,disable}_sagv() static

intel_{enable,disable}_sagv() are no longer needed outside the
compilation unit. Make them static.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200925121749.708-1-ville.syrjala@linux.intel.com


Reviewed-by: José Roberto de Souza <jose.souza@intel.com>