Add a new machine definition for Raspberry Pi 4 because it is
not present in branch thud of meta-raspberrypi. This machine
definition is taken from the master branch of the upstream of
Yocto/OE layer meta-raspberrypi.
Bug-AGL: SPEC-2656
Signed-off-by: Leon Anavi <leon.anavi@konsulko.com>
Change-Id: I368f6c7107ca023da66ce60d2006984f8939cf00