core: Add some static libraries

 * Add static versions of libdiskconfig and libsysutils for MiniVold

Change-Id: I9ea9498dcff3f094bbcbb1e05e6d10bc9b83ac74
sdcard: Allow building as a static library

 * Split main() out in order to allow linking with a multi-call
   executable such as recovery.

Change-Id: I3325135e47e4dd5af3912f5ce67ec64007d54a63