hw/arm/aspeed: Make aspeed_machine_class_init_cpus_defaults() globally accessible

hw/arm/aspeed: Make aspeed_machine_class_init_cpus_defaults() globally accessible

The function aspeed_machine_class_init_cpus_defaults() is now made
globally visible so that it can be used by other Aspeed machine C files.

Previously, this function was declared as static, restricting its
visibility to aspeed.c. Since future machine split files will also
need to call this helper to initialize default CPU settings, its
declaration has been moved to the common header aspeed.h and the
static keyword has been removed.

No functional changes.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20251104031325.146374-3-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>