Loading files

BIOS calls BIOSF_LOADFILE ($C00552) and BIOSF_LOADFILEX ($C00564) are used to load files from the CD.

The BIOSF_LOADFILE call displays a loading animation, while BIOSF_LOADFILEX (better name ?) doesn't.

Register A0 needs to point to a block indicating:
 * The filename, ended by a 0 byte
 * The bank number (8bit)
 * An optional pad byte to align:
 * Destination address (32bit)

The destination memory is automatically chosen according to the file's extension.

Rules:
 * SPR files have 1MiB banks. PCM files have 512KiB banks. Other types aren't banked.
 * FIX files and PCM files need to have their destination address multiplied by 2.

BIOS RAM adresses for currently loaded sectors, total sectors ?...