qemu: Add AAVMF to the list of known UEFIs

qemu: Add AAVMF to the list of known UEFIs

Well, even though users can pass the list of UEFI:NVRAM pairs at the
configure time, we may maintain the list of widely available UEFI
ourselves too. And as arm64 begin to rises, OVMF was ported there too.
With a slight name change - it's called AAVMF, with AAVMF_CODE.fd
being the UEFI firmware and AAVMF_VARS.fd being the NVRAM store file.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>