ide-cd: merge cdrom_rw_intr() and cdrom_newpc_intr()

Add handling of fs read/write requests to cdrom_nepwc_intr()
and remove no longer needed cdrom_rw_intr().

There should be no functionality changes caused by this patch.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>