Make the whole thing easier to read. While at it, make the parsing more
robust, and ensure we don't read past buffer being parsed.

v2: improve commit message (Daniel)
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452001851-8967-1-git-send-email-jani.nikula@intel.com