virt-manager: Add firmware preferences for creating a new VM

Possible values are BIOS (default) and UEFI.
The firmware used is determined by libvirt unless a specific firmware is
selected from the Customize dialog.

See https://bugzilla.redhat.com/show_bug.cgi?id=1997882

virtManager/createvm.py

@@ -478,7 +478,11 @@ class vmmCreateVM(vmmGObjectUI):
                 guest.os.is_ppc64() or
                 guest.os.is_s390x())
 
-        if guest.prefers_uefi():
+        default_efi = self.config.get_default_firmware_setting() == "uefi"
+        if default_efi:
+            log.debug("UEFI default requested via app preferences")
+
+        if guest.prefers_uefi() or default_efi:
             try:
                 # We call this for validation
                 guest.enable_uefi()