Changes include:
* gcc-10 compile fix
* NetBSD boot fix due to wrong power button address
* Fix endian bug in romfile_loadint()
* Introduce SeaBIOS firmware version check
* Implement QEMU fw_cfg interface support

Required for proper version checking and gcc-10 update on Debian.

Signed-off-by: Helge Deller <deller@gmx.de>