[coreboot] Improving KBC1126 support for HP laptops

[Iru Cai]

Hi,

I'm now doing the port for HP Elitebook 2760p (
https://review.coreboot.org/#/c/18241/) and other HP laptops, but I'm now
having trouble with the EC+SuperIO chip KBC1126.

Now I can use superio/smsc/kbc1100 to enable keyboard support. However, I
still cannot access the EC with ectool, which will give me all 0xff when I
run `ectool -d`. Also I cannot use the touchscreen even I write some ACPI
code.

I have searched and downloaded two SMSC confidential document: a KBC1122
preliminary datasheet and a KBC1122 BIOS porting guide. Is there any
problem if I use them to write some code?

Thanks,
Iru