Various block drivers implement the CDROMMULTISESSION,
CDROM_GET_CAPABILITY, and CDROMEJECT ioctl commands, relying on the
block layer to handle compat_ioctl mode for them.

Move this into the drivers directly as a preparation for simplifying
the block layer later.

When only integer arguments or no arguments are passed, the
same handler can be used for .ioctl and .compat_ioctl, and
when only pointer arguments are passed, the newly added
blkdev_compat_ptr_ioctl can be used.
Reviewed-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>