arch: mach-k3: j721s2_init: Disable the firewalls

Some firewalls enabled by ROM are still left on. So some
address space is inaccessible to the bootloader. For example,
in OSPI boot mode we get an exception and the system hangs.
Therefore, disable all the firewalls left on by the ROM.

Signed-off-by: Jayesh Choudhary <j-choudhary@ti.com>
Reviewed-by: Andrew Davis <afd@ti.com>
Reviewed-by: Manorit Chawdhry <m-chawdhry@ti.com>