fs_mgr: Support 16k F2FS

This passes the block size to mkfs. Currently f2fs must have page size
equal to block size. If this changes, we may want to revisit this.

Change-Id: I1ecdffcb2a271aa80c0bd07fd095941720fb48d0
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Bug: 279820706
Test: Boot 16K device