Like other Allwinner A64 boards, pinebook also need altering
auto-numbering of mmc2 to mmc1 which is available in common
sunxi dsti file, sunxi-u-boot.dtsi

Pinebook has a separate sun50i-a64-pinebook-u-boot.dtsi which
takes more precedence for u-boot.dtsi inclusion and it eventually
failed to include the sunxi-u-boot.dtsi.

So, this patch add support to include the sunxi-u-boot.dtsi in the
sun50i-a64-pinebook-u-boot.dtsi

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Vasily Khoruzhick <anarsoul@gmail.com> # Pinebook