Update darmgen.py

Make all variables in armv7-tbl.h extern'ed
Merge pull request #20 from djpnewton/patch-1

Make all variables in armv7-tbl.h extern
dropped reporting of mov[s] r0, r0 as NOP
Merge pull request #21 from pistol/master

dropped reporting of mov[s] r0, r0 as NOP
stupid fix for incorrect ldm simplifications to pop