arm: dts: k3-am654: include a53 board dtb for r5 build

To make things as organized as possible, start from the Linux board dtbs
and apply all properties needed for U-Boot in our *-u-boot.dtsi file for
the MAIN SPL and U-Boot builds.

We can then include these files for the WKUP SPL build making further
edits to the needed properties and nodes for the WKUP SPL bootloader's
view of the am65x.

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