[coreboot] [PATCH]nvramtool: Support CBFS Images in nvramtool

[Georgi, Patrick]

This is the first patch of this series that actually adds a new feature.
Use nvramtool -C to work on CBFS images that contain cmos_layout.bin for
CMOS metadata and cmos.default for CMOS defaults.
Read/Write/Enum on CMOS data work on cmos.default then.

Signed-off-by: Patrick Georgi