devices.xml: Added Sony Xperia U (kumquat)

Added Xperia U

model: ST25, ST25i, ST25a, Xperia U, kumquat
kernel partition: /dev/block/mmcblk0p9
recovery partion: /dev/block/mmcblk0p9 (we don't have independent recovery partition, so it's the same as kernel
cache partition: /dev/block/mmcblk0p12

system partition: /dev/block/mmcblk0p10
data partition: /dev/block/mmcblk0p11
modemfs partition: /dev/block/mmcblk0p6