Add option to build a UDF image

[JayFoxRox]

We've been having a bunch of problems with extract-xiso, so it would be nice if we could also build a Universal Disk Format image as alternative (this feature could be optional, if the user has mkisofs).

I believe I had successfully built a working image like this:

@mkisofs -UDF -o udf.iso $(OUTPUT_DIR)/

I assume that UDFs will be slower, because XISO has a search-tree, whereas UDFs only have arrays(?). But as a more reliable fallback it would be nice to have.

[InternalLoss]

Trying with nxdk's triangle demo on macOS 10.15.6 Beta (19G46c) - I had to install dvdrtools using brew, and also had to use -udf instead of -UDF - booted the disc using my 1.4 Xbox with an OpenXenium and EvoX M8+ works completely from the boot screen.

EDIT: Also launches fine from UnleashX, with it being detected as a Game correctly :p