Reset the CMOS based on a private flag. Tested on coreboot using an
offset of 123. Required when a CMOS layout or default option has
changed as the resulting flash will have 0's for the modified option.
As we are only writing to the BIOS region, we only need to backup the BIOS
region. The will avoid the error "failed to back up original firmware" if
regions such as the ME can't be read.
This change allows other device types to derive from common flashrom
code in the flashrom-device type.
Change-Id: Ic963fd586e0a73153c54889fce50055753a1bf5c
