drm/xe: Fix fault on fd close after unbind

In the Linux kernel, the following vulnerability has been resolved:

drm/xe: Fix fault on fd close after unbind

If userspace holds an fd open, unbinds the device and then closes it,
the driver shouldn't try to access the hardware. Protect it by using
drm_dev_enter()/drm_dev_exit(). This fixes the following page fault:

<6> [IGT] xe_wedged: exiting, ret=98
<1> BUG: unable to handle page fault for address: ffffc901bc5e508c
<1> #PF: supervisor read access in kernel mode
<1> #PF: error_code(0x0000) - not-present page
...
<4> xe_lrc_update_timestamp+0x1c/0xd0 [xe]
<4> xe_exec_queue_update_run_ticks+0x50/0xb0 [xe]
<4> xe_exec_queue_fini+0x16/0xb0 [xe]
<4> __guc_exec_queue_fini_async+0xc4/0x190 [xe]
<4> guc_exec_queue_fini_async+0xa0/0xe0 [xe]
<4> guc_exec_queue_fini+0x23/0x40 [xe]
<4> xe_exec_queue_destroy+0xb3/0xf0 [xe]
<4> xe_file_close+0xd4/0x1a0 [xe]
<4> drm_file_free+0x210/0x280 [drm]
<4> drm_close_helper.isra.0+0x6d/0x80 [drm]
<4> drm_release_noglobal+0x20/0x90 [drm]

(cherry picked from commit 4ca1fd418338d4d135428a0eb1e16e3b3ce17ee8)