blobutil: support fetching KBC1126 EC (HP laptops)

This is useful for e.g. HP EliteBook 2560p.

In coreboot config, enable e.g. (for lbmk blobutil):

CONFIG_KBC1126_FW1="../../ec/hp2560p/ec.bin.fw1"
CONFIG_KBC1126_FW2="../../ec/hp2560p/ec.bin.fw2"

In resources/blobs/sources you would have these entries:

EC_url
EC_url_bkup
EC_hash