Fix bug in CBFS file walking with compressed files.

The file walking code was incorrectly using the uncompressed file size
when searching for the next file.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Support custom boot menu prompt and custom boot menu key.

Allow configuration of the boot menu prompt and boot menu key (via the
romfile interface).  Some machines don't have an F12 key, so make this
configurable.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
acpi_extract.py: document DEVICE directives

commit 2b568ebb20b08c7881d976b5bc9f59a425bae5e6
    acpi_extract: detect DeviceOp
added new directives to acpi_extract.py, but didn't
document them.
Add documentation at top of file.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>