[media] mceusb: select default keytable based on vendor

Some vendors have their on keymap table that are used on
all (or almost all) models for that vendor.

So, instead of specifying the keymap table per USB ID,
let's use the Vendor ID's table by default.

At the end, this will mean less code to be added when newer
devices for those vendors are added.

Of course, if rc_map is specified per board, it takes
precedence.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>