QEMU: support UEFI via -bios

[arixmkii]

Description

Add configuration option to load UEFI firmware through -bios command line option. It is not really needed for the currently supported platforms, but on Windows WHPX acceleration experiencing issues with pflash mounted firmware https://gitlab.com/qemu-project/qemu/-/issues/513 Patch exists to workaround this, but using out of tree patches is a complication on its own. There is a workaround provided to load concatenated vars and code via -bios.

Current proposal:

• add flag under Firmware section similar to LegacyBIOS
• default value is false or false for non-windows OSes if this is possible/suitable
• add code path to lookup vars counterpart (this is a bit trickier than code, because x86_64 is using vars of i386, but could be handled with trivial conditional reasoning)
• generate concatenated version in the machine working directory
• generate QEMU command line based on the flag

End goal - support upstream QEMU builds with Lima on Windows hosts.

I plan to work on this feature.

[arixmkii]

Later, if the issue is fixed upstream, the introduced flag could be deprecated/discouraged and eventually removed, when the minimal supported version is bumped.