f2fs-tools: fix build system to make distcheck correctly

f2fs-tools: fix build system to make distcheck correctly

The current build system fails to `make distcheck` correctly
for two reasons: 1) Some header files are not listed in the
source files for fsck.f2fs and mkfs.f2fs, and so don't make it
into the dist tarball.  2) By setting a default prefix in
configure.ac, the mock install doesn't add the correct prefix
and instead tries to install directly to the file system.

This patch corrects those problems and also adds an autogen.sh
script for convenience.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>