gpio: aspeed: Create llops to handle hardware access

Add low-level operations (llops) to abstract the register access for GPIO
registers and the coprocessor request/release. With this abstraction
layer, the driver can separate the hardware and software logic, making it
easier to extend the driver to support different hardware register
layouts.

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
Reviewed-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Tested-by: Andrew Jeffery <andrew@codeconstruct.com.au> # AST2600
Link: https://lore.kernel.org/r/20241008081450.1490955-6-billy_tsai@aspeedtech.com


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>