started unification of floppy and ramdisk code

src/dos_m65/unit_disk/unit_fd_cmd_close.s

@@ -0,0 +1,13 @@
+
+;
+; Close currently opened file
+;
+
+
+unit_fd_cmd_CLOSE:
+
+	; XXX provide implementation
+
+	jsr lowlevel_fdc_motor_off         ; disable drive motor  XXX only do this if no channel is opened
+
+	jmp dos_EXIT_SEC