board/udoo: use common freescale infrastructure

board/udoo: use common freescale infrastructure

U-Boot 2020.10 no longer provides boot command in default environment for
Udoo Quad/Dual board. Boot script needs to be added to the image. In order
to keep using common infrastructure for freescale boards, move boot files
to root filesystem and add boot script there. Also switch Udoo Neo board
to common freescale infrastructure to simplify maintenance.

Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>