arm: mach-k3: Increase SYSFW max image size

When booting with HS silicon, the system firmware image is 278270, which
is slightly larger than currently allocated amount.

This can cause unexpected behavior if this overlap interferes with other
things in memory, so increase this with a slightly margin added as well
to avoid any boot issues that can appear after system firmware gets
loaded.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Tero Kristo <kristo@kernel.org>
Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>
Reviewed-by: Dhruva Gole <d-gole@ti.com>