Allow finding uefi firmware for qemu windows

[afbjorklund]

The files are located in C:\Program Files\qemu\share on Windows.

For some reason*, using pflash doesn't work - only old bios flag.

---

I'm not sure the default files work, had provide a custom OVMF_CODE.fd

* Issue being tracked at: https://gitlab.com/qemu-project/qemu/-/issues/513

[AkihiroSuda]

Is this still draft?

[afbjorklund]

I left all the Windows patches in "draft" for early review, until they can be completed "properly"

The problem with this -bios workaround was that it required a custom firmware file - not the edk2 bundled with qemu...