Change in coreboot[master]: mb/google/dedede/var/magolor: Set core display clock to 172.8 MHz

[Ren Kuo (Code Review)]

Attention is currently required from: Nico Huber, Henry Sun, Paul Menzel, Angel Pons, Simon Yang, Kane Chen, Karthik Ramasubramanian.
Ren Kuo has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/60301 )

Change subject: mb/google/dedede/var/magolor: Set core display clock to 172.8 MHz
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Patch Set 9:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/60301/comment/20b2b377_dd0899e3 
PS6, Line 13: recommendation. (refer to src/soc/intel/jasperlake/chip.h)
> What frequency is chosen by default? And why is FSP choosing a higher than […]

From CL:60009 's comment:
=> Is this the default config in FSP?
Yes, 0xff is the default value of setting CdClock.
=> Are you planning to upload a follow-up change for Magolor?
No, I will leave it for ODM to adjust it.

The default value in FSP is as before,and keep the CdClock=0xff in baseboard devicetree. 
It will not impact all current dedede projects firmware by the change.

For ODM owners, we can overwrite a tuning value in dedede/variant/xxxx devicetree if it's necessary.