KVM host support was recently enabled in ppc44x_defconfig, but since then the
config option was renamed. Update ppc44x_defconfig to match.

Also, KVM guests aren't very interesting without networking, so enable
CONFIG_TUN and CONFIG_BRIDGE.
Signed-off-by: NHollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: NJosh Boyer <jwboyer@linux.vnet.ibm.com>