Makefile: Add rockchip image type

Add rockchip image type support. right now the image
type marked with rksd, So create image type variable
with required image type like rksd or rkspi.

Cc: Matwey V. Kornilov <matwey.kornilov@gmail.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
1 file changed