hw/arm/aspeed_ast27x0-fc: Map ca35 memory into system memory

hw/arm/aspeed_ast27x0-fc: Map ca35 memory into system memory

Map the CA35 memory region as a subregion of system_memory to ensure
a valid FlatView. This prevents failures in APIs that rely on the
global memory view, such as rom_check_and_register_reset().

Signed-off-by: Steven Lee <steven_lee@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250523093144.991408-5-steven_lee@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>