hw/arm/aspeed: Move aspeed_install_boot_rom to common SoC code

hw/arm/aspeed: Move aspeed_install_boot_rom to common SoC code

Move the boot ROM install helper into common SoC code so it can be reused
by all ASPEED boards, and decouple the API from AspeedMachineState.

Specifically:
 - Move aspeed_install_boot_rom() to hw/arm/aspeed_soc_common.c and
   declare it in include/hw/arm/aspeed_soc.h.
 - Change the helper’s signature to take AspeedSoCState * and a
   MemoryRegion * provided by the caller, instead of AspeedMachineState *.
 - Update aspeed_machine_init() call sites accordingly.

No functional change.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250925050535.2657256-4-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>