drm/xe/guc_pc: move pc_fini to devm

Here we are touching the HW/GuC and presumably this should happen when
the device is removed. Currently if you hotunplug the device this is
skipped if there is already open driver instance.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240522102143.128069-24-matthew.auld@intel.com