mmc: Enable support for Triangle Away

Exposes /dev/block/mmcblk0boot0 and /dev/block/mmcblk0boot1, where
the custom binary flash count is stored.  Re-exposing these enables
the use of utilities like Triangle Away to reset the counter.

Origin : https://github.com/CyanogenMod/android_kernel_samsung_smdk4210/commit/5025d575e228923211ae5fcda2a1bb348756f913