V4L/DVB: IR: add helper function for hardware with small o/b buffer

Some ir input devices have small buffer, and interrupt the host
each time it is full (or half full)

Add a helper that automaticly handles timeouts, and also
automaticly merges samples of same time (space-space)
Such samples might be placed by hardware because size of
sample in the buffer is small (a byte for example).

Also remove constness from ir_dev_props, because it now contains timeout
settings that driver might want to change

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Acked-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>