gem5: update to 1db7ecb4ce46e4ea525e6564032b4486c72c1c41

M5_PATH is not needed anymore, get rid of it!

run

@@ -486,7 +486,6 @@ Extra options to append at the end of the emulator command line.
             gem5_exe_args = self.sh.shlex_split(self.env['gem5_exe_args'])
             if do_trace:
                 gem5_exe_args.extend(['--debug-flags', trace_type, LF])
-            extra_env['M5_PATH'] = self.env['gem5_system_dir']
             # https://stackoverflow.com/questions/52312070/how-to-modify-a-file-under-src-python-and-run-it-without-rebuilding-in-gem5/52312071#52312071
             extra_env['M5_OVERRIDE_PY_SOURCE'] = 'true'
             if self.env['trace_stdout']:
@@ -624,6 +623,9 @@ Extra options to append at the end of the emulator command line.
                             ),
                             LF
                         ])
+                if self.env['gem5_script'] == 'fs' or self.env['gem5_script'] == 'biglittle':
+                    if self.env['gem5_bootloader'] is not None:
+                        cmd.extend(['--bootloader', self.env['gem5_bootloader'], LF])
             cmd.extend(['--mem-size', memory, LF])
             if self.env['gdb_wait']:
                 # https://stackoverflow.com/questions/49296092/how-to-make-gem5-wait-for-gdb-to-connect-to-reliably-break-at-start-kernel-of-th