INT 2F U - PCIBM PC Tools v8.0 DRIVEMAP - SET DRIVE MAPPING
	AX = 920Bh
	BL = drive letter (41h ['A'] = A:, etc)
	CX = ??? (0000h removes mapping)
Return: AX = ??? or FFF8h on error
SeeAlso: AX=9201h,AX=920Dh