Arm backend: Add devtools support to example

New flags on run.sh
--etdump
  Build in etdump and profiling, the etdump base64 coded and put in
  the log
--debug_build
  Build debug instead of release
--extra_build_flags
  Extra flags to pass to cmake this makes it for example possible to
  override the allocator pool size or other build time cmake flags.

The devtools build has been updated so FLATCC_EXECUTABLE can be used
to point out the executable.

Signed-off-by: Zingo Andersen <zingo.andersen@arm.com>
Change-Id: Ic0fb1e48ee633c5fe91473bdc2db9e894b2fc4fa