Add RIL_REQUEST_EMERGENCY_DIAL string in rillog

This will let riljLog display this request in the log and bugreport,
 and maybe helpful for some tools that parses this log.

Test: Treehugger; Manual
Fixes: 134704399
Change-Id: Idc724ff5363e7459e291ffb13d955003a1ba6655
Merged-In: Idc724ff5363e7459e291ffb13d955003a1ba6655
(cherry picked from commit e615fe81)