Adds generate_bindings.sh script which will

Adds generate_bindings.sh script which will
do the following for pyangbind project.

* Downloads YANG dependency files, from lispflowmapping
  into the odl-lispflowmapping-yang-files directory in
  the same directory i.e. odl-lispflowmapping-yang-bindings
  as the script;

* Generate the LISPFlowMappingYANGBindings.py into the
  same directory i.e. odl-lispflowmapping-yang-bindings
  so that in the later code for generating JSON dictionaries
  we can assume it is there.

* Adds bits.patch, Currently pyangbind doesn't support
  bits type so this patch would comment all those
  cases from yang files for pyangbind to generate the
  bindings file.

Change-Id: I6ec4af7060019b805f75d9a4b11bedf224fe6f77
Signed-off-by: Ashish <ashishk.iiit@gmail.com>