V4L/DVB (13532): ir-common: Add infrastructure to use a dynamic keycode table

V4L drivers use an static keycode vector with 128 entries, where the scancode
indexes the keycode. While this works, it limits the scancodes to have only
7 bits, not allowing for example full RC5 codes.

Instead of implementing the same code on every V4L driver, provide a common
infrastructure to handle the bigger tables, minimizing the changes inside
each driver.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>