Add the Greybus controller HAL

Add the controller HAL in order to add support of Greybus
to different type of device such as bluetooth or Wi-Fi.
SVC and Greybus (through Netlink) use interface and cport,
and the controller HAL will convert it in some way to be
compatible with bluetooth, Wi-Fi, etc.

Signed-off-by: Alexandre Bailon <abailon@baylibre.com>