Change in coreboot[master]: apple/macbook21: configure the clockgen and add C3 CPU state

[Arthur Heymans (Code Review)]

Attention is currently required from: Ferass EL HAFIDI, Evgeny Zinoviev.
Arthur Heymans has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/63587 )

Change subject: apple/macbook21: configure the clockgen and add C3 CPU state
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Patch Set 4:

(1 comment)

File src/mainboard/apple/macbook21/Kconfig:

https://review.coreboot.org/c/coreboot/+/63587/comment/3d9d23c0_3bfd7301 
PS4, Line 19: DRIVERS_I2C_CK505
> I'm thinking about this: since the board is similar (if not exact) it should have a compatible clockgen but I don't have an iMac5,2 so I can't test. Also on most desktops there's no C2 or C3 so that might be the case on the iMac5,2 but I can't test. :/
> I probably should make the coreboot build system use those drivers only on MacBook2,1 and MacBook1,1 laptops.

Imac5.2 uses CY285566 and macbook21 uses SLG8LP436. I think it's better to guard the imac from setting up a possible wrong configuration. You can do that in the Kconfig file with 'select DRIVERS_... if !BOARD_APPLE_IMAC52' . You'd also need to use #if !CONFIG(BOARD_APPLE_IMAC52) ... in the C file to guard against using C3.