Add Lohit-Tamil.ttf and Lohit-Bengali.ttf to Fallback list

Bug: 5370370

Lohit-Tamil.ttf and Lohit-Bengali.ttf were added to the system
image in CL 4baaa05f0383bee670a0bebc177b94a1c119eab7 but did not
get added to the fallback_fonts.xml file, so skia will never find
these fonts.  This CL will not increase the sysetm image size, it
will simply let Skia find these fonts.

Change-Id: I85b3c191c278181ee36a88841832dcfba0bab886