modules/firmware: add a new option to denote a firmware group to choose one.

This adds a tag that will go into the module info, only one firmware from
the group given needs to be available for this driver to work. This allows
dracut to avoid adding in firmware that aren't needed.

This just brackets a module list in the modinfo, the modules in the list
will get entries in reversed order so the last module in the list is the
preferred one.

The corresponding dracut code it at:
dracutdevs/dracut#2309

Cc: Luis Chamberlain <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Dave Airlie <[email protected]>

Author: airlied

include/linux/module.h

@@ -290,6 +290,8 @@ extern typeof(name) __mod_##type##__##name##_device_table		\
  * files require multiple MODULE_FIRMWARE() specifiers */
 #define MODULE_FIRMWARE(_firmware) MODULE_INFO(firmware, _firmware)
 
+#define MODULE_FIRMWARE_GROUP_ONLY_ONE(_grpname) MODULE_INFO(firmware_group_only_one, _grpname)
+
 #define MODULE_IMPORT_NS(ns)	MODULE_INFO(import_ns, __stringify(ns))
 
 struct notifier_block;