arm: dts: k3-am654-r5: Merge board file and U-Boot overlay

The R5 board file for U-Boot should be the same as the board file copied
from Linux with a few alterations to work with the R5's view of the SoC.

First we need to unify the R5 board file and it's U-Boot overlay before
we can unify the Linux board file with this one.

Tested-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Bryan Brattlof <bb@ti.com>
Reviewed-by: Nishanth Menon <nm@ti.com>