[backlog] Add Xenomai4 (EVL) Support

Xenomai4 does not have RTDM, but instead some additional members of file_operations struct:

struct file_operations {
	...
	ssize_t (*oob_read) (struct file *, char __user *, size_t);
	ssize_t (*oob_write) (struct file *, const char __user *, size_t);
	long (*oob_ioctl) (struct file *, unsigned int, unsigned long);
	long (*compat_oob_ioctl) (struct file *, unsigned int, unsigned long);
	__poll_t (*oob_poll) (struct file *, struct oob_poll_wait *);
	...
} __randomize_layout;

Please note that adding EVL support is currently not planned from our side, but contributions are welcomed.