arm: boot: Adjust indentation of FIXUP comments

These comments start immediately after the current longest name in the
list. Tab them out to the next tab stop to give a little breathing room
and prepare for FIXUP_BOARD_SETUP which will require more indent.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Message-id: b9b9bb8f1c307c1ef8a3f26ff1f34fabb34b332e.1446182614.git.crosthwaite.peter@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>