[L] Change in coreboot[main]: mainboard: add Dell Latitude E7240

[Iru Cai (Code Review)]

Iru Cai has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/79746?usp=email )

Change subject: mainboard: add Dell Latitude E7240
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Patch Set 1:

(1 comment)

Patchset:

PS1: 
This is a rework of CB:40300 based on the latest code. I don't know why gerrit doesn't use CB:40300 while the Change-Id doesn't change.

I reuse ec/dell/mec5035, but it doesn't boot when I use it in the devicetree, so the touchpad still doesn't work.