kernel-doc: xforms: support __SYSFS_FUNCTION_ALTERNATIVE()

kernel-doc: xforms: support __SYSFS_FUNCTION_ALTERNATIVE()

Add support for __SYSFS_FUNCTION_ALTERNATIVE() to create a union of its
members (as though CONFIG_CFI is unset).

Fixes these docs build warnings:

WARNING: include/linux/device.h:117 Invalid param: __SYSFS_FUNCTION_ALTERNATIVE( ssize_t (*show)(struct device *dev, struct device_attribute *attr, char *buf)
WARNING: include/linux/device.h:117 struct member '__SYSFS_FUNCTION_ALTERNATIVE( ssize_t (*show' not described in 'device_attribute'
WARNING: include/linux/device.h:117 Invalid param: __SYSFS_FUNCTION_ALTERNATIVE( ssize_t (*store)(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
WARNING: include/linux/device.h:117 struct member '__SYSFS_FUNCTION_ALTERNATIVE( ssize_t (*store' not described in 'device_attribute'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260623190006.406571-1-rdunlap@infradead.org>