gpio: aspeed-sgpio: Convert IRQ functions to use llops callbacks

gpio: aspeed-sgpio: Convert IRQ functions to use llops callbacks

Update aspeed_sgpio_irq_handler() and aspeed_sgpio_setup_irqs() to use
the llops callbacks for register access instead of direct iowrite32().
This creates a unified hardware access layer, which is essential for
supporting SoCs with different register layouts like the AST2700.

Additionally, change the loop bounds to use ngpio instead of the static
ARRAY_SIZE(aspeed_sgpio_banks). This allows the driver to adapt to the
actual number of supported pins on the running SoC.

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
Link: https://lore.kernel.org/r/20260123-upstream_sgpio-v2-4-69cfd1631400@aspeedtech.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>