arm: dts: k3-j721e-r5: Remove MAIN R5FSS0 cluster from SPL

The MAIN R5FSS0 cluster and corresponding nodes are no longer required
to be enabled in R5 SPL after removing the support for booting any core
from this cluster on R5 SPL. So, remove these from the relevant dts
files.

This is essentially a revert of the additions done in commit 2984b82b
("arm: dts: k3-j721e-r5: Enable r5fss0 cluster in SPL").

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210726211311.5977-5-s-anna@ti.com