arm: dts: k3-j7200: Fix up MAIN R5FSS cluster mode back to Split-mode

arm: dts: k3-j7200: Fix up MAIN R5FSS cluster mode back to Split-mode

The default U-Boot environment variables and design are all set up for
the MAIN R5FSS cluster to be in Split-mode. This is the setting used
when the dts nodes were originally added in v2021.01 U-Boot and the
dt nodes are synched with the kernel binding property names in
commit 468ec2f3ef8f ("remoteproc: k3_r5: Sync to upstreamed kernel DT
property names") merged in v2021.04-rc2.

The modes for the MAIN R5FSS cluster got switched back to LockStep mode
by mistake in commit fa09b12dc5f6 ("arm: ti: k3: Resync dts files and
bindings with Linux Kernel v5.14") in v2022.01-rc1. This throws the
following warning messages when early-booting the cores using default
env variables,

k3_r5f_rproc r5f@5d00000: Invalid op: Trying to start secondary core 7 in lockstep mode
Load Remote Processor 3 with data@addr=0x82000000 83148 bytes: Failed!

Fix this by switching back both the clusters to the expected Split-mode.
Make this mode change in the u-boot specific dtsi file to avoid such
sync overrides in the future until the kernel dts is also switched to
Split-mode by default.

Fixes: fa09b12dc5f6 ("arm: ti: k3: Resync dts files and bindings with Linux Kernel v5.14")
Signed-off-by: Suman Anna <s-anna@ti.com>