Script: Fix disassemble_tombstone.py

Update for newer debuggerd output marking the memory dump around
the currently executed code.

Add a hack for ARM assembly: override the assembler-emitted $d
symbol marking all our .byte data, so that objdump will disassemble
as instructions.

Test: manual
Change-Id: I100ed9e0ce39c073d5885cc430d78c24fef38882