Append disc label to the first disc of two-disc games too, rather than
only labelling the second disc.

Same behavior, but less code.

DiscIO: Add support for the NFS format

Previously, we had WBFS and CISO which both returned an upper bound
of the size, and other formats which returned an accurate size. But
now we also have NFS, which returns a lower bound of the size. To
allow VolumeVerifier to make better informed decisions for NFS, let's
use an enum instead of a bool for the type of data size a blob has.

This means that dol/elf files with upercase extensions (e.g. BOOT.DOL) are properly detected.