buildroot

infra: Add POST_RSYNC_HOOKS support

One of the use cases is for the 'local packages' to restore
the SCM info.  Some packages use this information to generate
version info during build time.  In this case, the local package
can have this hook to restore it by symbolic link for example.

[Thomas: update commit title]
Signed-off-by: Tzu-Jung Lee <tjlee@ambarella.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>