drm/xe/xe_gt_idle: modify powergate enable condition

drm/xe/xe_gt_idle: modify powergate enable condition

Modify powergate enable condition based on the type of GT or presence of
media engines. Also have a copy of the value written to powergate enable
register.

v2: add condition to enable render or media powergating (Badal)

v3: fix commit message (Shekhar)
    fix kernel-doc

Signed-off-by: Riana Tauro <riana.tauro@intel.com>
Reviewed-by: Shekhar Chauhan <shekhar.chauhan@intel.com>
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240906071126.28078-2-riana.tauro@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>