drm/i915: Handle each GT on init/release and suspend/resume

In preparation for enabling a second GT, there are a number of GT/uncore
operations that happen during initialization or suspend flows that need
to be performed on each GT, not just the primary,

Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220906234934.3655440-10-matthew.d.roper@intel.com
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>