generic: platform/mikrotik: use MTD notifier

generic: platform/mikrotik: use MTD notifier

If the SPI probe is sufficiently delayed, the routerboot driver may fail
to init as the routerboot partitions are not yet available.

Register an MTD user notifier instead of doing straight init so that the
init subroutines are only executed when the target MTD partitions are
present.

Because the init/exit routines can now be called outside of the kernel
normal init/exit calls, they cannot be jettisoned and must always be
available: the __init and __exit qualifiers are thus removed.

Reported-by: Denis Kalashnikov <denis281089@gmail.com>
Signed-off-by: Denis Kalashnikov <denis281089@gmail.com>
Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>
Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
[bump hardconfig/softconfig versions]
Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>