sdcard: Add support for sdcardfs!

 * sdcardfs is a kernel filesystem developed by Samsung and recently
   seen in AOSP's common kernel branches. It entirely eliminates
   the need to use FUSE for sdcard emulation and moves all the
   wrapping logic to kernel. This vastly improves performance for
   use cases which read/write to emulated as well as removable
   cards.

Change-Id: I3e394a99e0a4b5beacaeddc0d4dd4855ff0cf082