drm/i915: Move GT powersaving init to i915_gem_init()

drm/i915: Move GT powersaving init to i915_gem_init()

BugLink: https://bugs.launchpad.net/bugs/1862840
GT powersaving is tightly coupled to the request infrastructure. To
avoid complications with the order of initialisation in the next patch
(where we want to send requests to hw during GEM init) move the
powersaving initialisation into the purview of i915_gem_init().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171110142634.10551-3-chris@chris-wilson.co.uk
CVE-2020-8832

(cherry picked from commit f58d13d5717938d4dfcc82a2eeba0a6d7644f6e5)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Timo Aaltonen <timo.aaltonen@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>