arm: dts: k3: use SPL_TEXT_BASE for R5 SPL load address

arm: dts: k3: use SPL_TEXT_BASE for R5 SPL load address

The load address for the R5's SPL is defined in Kconfig by
SPL_TEXT_BASE. Rather than hard coding the load address which could
lead to hard to debug issues if this value is changed, just use the
SPL_TEXT_BASE value.

Reviewed-by: Andrew Davis <afd@ti.com>
Signed-off-by: Bryan Brattlof <bb@ti.com>
Reviewed-by: Neha Malcom Francis <n-francis@ti.com>