drm/i915: Rename and expose common GT early init routine

drm/i915: Rename and expose common GT early init routine

The common early GT init is needed for initialization of all GT types
(root/primary, remote tile, standalone media).  Since standalone media
(coming in a future patch) will be implemented in a separate file,
rename and expose the function for use.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220906234934.3655440-7-matthew.d.roper@intel.com
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>