V4L/DVB: ir-core: move rc map code to rc-map.h

The keymaps don't need to be recompiled every time a change at ir-core.h
happens, since it only depends on rc-map defines. By moving those
definitions to the proper header, the code became cleaner, and avoids
needing to recompile all the RC maps every time a non-related change
is introduced.

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