ODROID-C1: cec: LG Simplink support

This change enables HDMI-CEC feature on LG TV. LG Simplink uses extra
VENDOR_COMMAND for HDMI-CEC. This patch adds some handling routines for
LG Simplink.

Change-Id: Ic2bbf75759cf1e3bfab98da7db3b912356a79358
Signed-off-by: Brian Kim <brian.kim@hardkernel.com>