dt-bindings: mfd: ti,j721e-system-controller: Add compatible strings for other platforms

There are multiple J7 based platforms, and the j721e-system-controller
shouldn't be define in non-j721e devices device trees.

This is mainly for clarity; but also useful in case there are future
erratas that need to be fixed for a specific platform.

Signed-off-by: Matt Ranostay <mranostay@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221024035405.366208-2-mranostay@ti.com