dt-bindings: add vendor prefix for Lichee Pi

Lichee Pi is a new "Pi"-named development board series.

Currently available device, Lichee Pi One, is by only one person as
night job, so the device series name is chosen to be the vendor prefix.

Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>