autofs: new package

Tested on i.MX6 using NFS mounts only. Not tested with DAS mounts as
of this commit.

[Thomas:
 - remove the "# rpcbind" comments on the thread and mmu dependencies,
   since we don't select rpcbind. The thread and mmu dependencies are
   still needed though, since autofs uses pthread_*() functions and
   fork().
 - Remove "Requires a toolchain with native RPC." in the Config.in
   help text and instead add a proper Config.in comment about the
   thread and RPC dependency.
 - Add patch to fix building with uClibc, taken from OpenEmbedded.]

Signed-off-by: Jonathan Ben Avraham <yba@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>