[S] Change in coreboot[master]: mb/google/myst: Add FW_CONFIG

[Jon Murphy (Code Review)]

Attention is currently required from: Raul Rangel, Eric Lai, Karthik Ramasubramanian, Mark Hasemeyer.

Jon Murphy has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/74102 )

Change subject: mb/google/myst: Add FW_CONFIG
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Patch Set 21:

(1 comment)

File src/mainboard/google/myst/variants/myst/overridetree.cb:

https://review.coreboot.org/c/coreboot/+/74102/comment/6951e913_681c52f9 
PS4, Line 20:
> e.g. https://review.coreboot. […]

EMMC's are on a bayhub nvme bridge, and for the most part to us they're just slightly different nvme.  We don't need a specific fw_config for it.  This is how we worked it on Skyrim as well.  OEM's may choose to handle it differently, but our preference is not to.  In general we only add FW_CONFIG items if they can't be derived or probed otherwise, or affect boot performance.