[POWERPC] Add DOS partition table support to mpc834x_itx_defconfig

The default configuration file for the MPC8349E-mITX reference board,
mpc834x_itx_defconfig, did not include support for DOS partition table types.
This support is necessary because the hard drive that comes with the ITX
is formatted with this partition table type.  Without this config option,
no partitions on the drive can be mounted.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>