[M] Change in coreboot[main]: soc/mediatek: Remove redundant struct pad_func and PAD_* definitions

[Yu-Ping Wu (Code Review)]

Attention is currently required from: Hung-Te Lin, Xi Chen, Yidi Lin.

Yu-Ping Wu has posted comments on this change by Yidi Lin. ( https://review.coreboot.org/c/coreboot/+/84222?usp=email )

Change subject: soc/mediatek: Remove redundant struct pad_func and PAD_* definitions
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Patch Set 2:

(3 comments)

File src/soc/mediatek/common/include/soc/gpio_common.h:

https://review.coreboot.org/c/coreboot/+/84222/comment/ca0bc676_9ebefd49?usp... :
PS2, Line 59: 	
`(struct pad_func)` to ensure the correct type. Same for the other macros below.

https://review.coreboot.org/c/coreboot/+/84222/comment/d25da007_0c93ce1e?usp... :
PS2, Line 59: }
Is it reasonable to have `GPIO_PULL_DOWN` as the default? I wonder if we could replace `PAD_FUNC` and `PAD_FUNC_SEL` with `PAD_FUNC_DOWN` and `PAD_FUNC_UP`.

https://review.coreboot.org/c/coreboot/+/84222/comment/b278ac49_c5f22ec1?usp... :
PS2, Line 59: PAD_##name##_FUNC_##func
These are defined in the `PIN()` macro in gpio_defs.h, so I'd prefer putting the definition and references in the same file. One way is to define `#define GPIO_PAD_FUNC(name, func) PAD_##name##_FUNC_##func` in gpio_defs.h, and use `GPIO_PAD_FUNC` here. Another solution is to simply move everything to a single file (either here or gpio_defs.h).