Change in coreboot[master]: soc/mediatek/mt8186: Add a stub implementation of the MT8186 SoC

[Yu-Ping Wu (Code Review)]

Attention is currently required from: Hung-Te Lin, Paul Menzel, Rex-BC Chen, Felix Held.
Yu-Ping Wu has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/58640 )

Change subject: soc/mediatek/mt8186: Add a stub implementation of the MT8186 SoC
......................................................................

Patch Set 3: Code-Review+2

(2 comments)

Commit Message:

https://review.coreboot.org/c/coreboot/+/58640/comment/1baaa0fe_312710e1 
PS2, Line 10:
> And that is big problem, and has to be improved. […]

Rex, could you add a short paragraph explaining the similarities and differences between mt8186 and existing SoCs (mt8183/mt8192)? Example for the timer:

Similar to MT8195, MT8186 uses v2 timer.

File src/soc/mediatek/mt8186/include/soc/timer.h:

https://review.coreboot.org/c/coreboot/+/58640/comment/4159d080_268b94d4 
PS3, Line 9: TIE_0_EN = 1 << 3,
           : 	COMP_15_EN = 1 << 10,
           : 	COMP_20_EN = 1 << 11,
           : 	COMP_25_EN = 1 << 12,
Rex, if these constants are always the same for platforms using v2 timer, please move them into timer_v2.h. If these happen to the same as in mt8195, we should keep them here.