Porting coreboot to HP Elitebooks

The HP Elitebook patches are finally merged to upstream yesterday.

Now I'm going to upload the board status and write documents to the wiki.

There are still some tasks to do. The digitizer in Elitebook 2760p doesn't work. GRUB payload will freeze. So I'm going to dig in the problems when I have time.

At last, I found a bit in EC RAM that is used to enable EC ACPI, so ACPI is working now. I copied the ASL code from vendor DSDT, and now battery, AC, and lid status change can be detected by OS now.

https://review.coreboot.org/#/c/19072/