sama5d4ek: use linux-yocto-custom instead of linux-atmel

This patch add sama5d4ek support for linux-yocto-custom. Then, use
linux-yocto-custom instead of linux-atmel.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
linux: remove linux-atmel as we can just use linux-yocto-custom

Since the linux-atmel is only for sama5d4ek board. Now as sama5d4ek
board uses linux-yocto-custom. So we can remove linux-atmel bb file.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
u-boot-at91: add sama5d4-xplained board git repo

Signed-off-by: Josh Wu <josh.wu@atmel.com>
at91bootstrap: add support for sama5d4 xplained board

Signed-off-by: Josh Wu <josh.wu@atmel.com>
linux-yocto-custom: add sama5d4 xplained board support

Also add the defconfig for sama5d4 xplained board.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
sama5d4-xplained: support new machine: sama5d4 xplained Ultra

Signed-off-by: Josh Wu <josh.wu@atmel.com>
videoplayer: for sama5d4-xplained board, we need use pda4 screen

Signed-off-by: Josh Wu <josh.wu@atmel.com>
videoplayer: sama5d4-xplained: Use plan B version which's without audio

As sama5d4-xplained board has no audio. So use PLAN B version.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
README: update to add sama5d4-xplained support

Signed-off-by: Josh Wu <josh.wu@atmel.com>
at91-bsp: bump version of at91bootstrap, u-boot and kernel

Signed-off-by: Josh Wu <josh.wu@atmel.com>
at91bootstrap: bump to v3.7.1

Signed-off-by: Josh Wu <josh.wu@atmel.com>
linux-yocto-custom: bump to SRCREV for sama5d4 xplained board

Signed-off-by: Josh Wu <josh.wu@atmel.com>