LVMv2: change default_data_alignment

-According to https://raw.github.com/steven676/android-lvm-mod/master/HOWTO-MOD
the default_data_alignment parameter should be our devices
"erase block size" and that the erase block size can be found by
cat /sys/block/mmcblk0/device/preferred_erase_size. I get a value of
2097152 which is exactly 2MB.

-I looked for this value before the initial LVMv2 implementation but
was unable to find it.
boardconfig: Align graphics values with Slim crespo device tree

-We have the same gpu as the (Nexus S) aka crespo.