[media] ir-rx51: Adjust dependencies

Although this kind of IR diode circuitry is known to exist only in
N900 hardware, nothing prevents making similar circuitry on any OMAP
based board. The MACH_NOKIA_RX51 dependency is thus not something we
want to be there.

Also, this should depend on LIRC as it is a LIRC driver.

Signed-off-by: Timo Kokkonen <timo.t.kokkonen@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>