drm/xe: Support 'nomodeset' kernel command-line option

drm/xe: Support 'nomodeset' kernel command-line option

Setting 'nomodeset' on the kernel command line disables all graphics
drivers with modesetting capabilities, leaving only firmware drivers,
such as simpledrm or efifb.

Most DRM drivers automatically support 'nomodeset' via DRM's module
helper macros. In xe, which uses regular module_init(), manually call
drm_firmware_drivers_only() to test for 'nomodeset'. Do not register
the driver if set.

v2:
- use xe's init table (Lucas)
- do NULL test for init/exit functions

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240827121003.97429-1-tzimmermann@suse.de
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>