V4L/DVB (12566): ir-keymaps: Fix IR mappings for channel and volume +/- keys

Use standard definitions for channel controls, as defined at:
	http://linuxtv.org/wiki/index.php/Remote_Controllers



While here, fix a few broken up/down/left/right mappings

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