hw/intc/aspeed: Support setting different register size

hw/intc/aspeed: Support setting different register size

Currently, the size of the regs array is 0x2000, which is too large. So far,
it only use GICINT128 - GICINT134, and the offsets from 0 to 0x1000 are unused.
To save code size, introduce a new class attribute "reg_size" to set the
different register sizes for the INTC models in AST2700 and add a regs
sub-region in the memory container.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250307035945.3698802-5-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>