misc: add clang format stylesheet

- Run to clang-format all committed files.
- Run with --all to format all cpp|cxx|cc|h|hpp|mm files in src/.
- Run with --install to install as a pre-commit hook.

Requires that clang-format be installed.

Devs should either install the pre-commit hook or configure their
editors to format on save etc.

Change-Id: I73c2b19e0673115c1f7d33cbae5094f3a88d43e3