siemens:cosmetic, dxr2: rename dxr2 to draco

siemens:cosmetic, dxr2: rename dxr2 to draco

The actual board name is draco and dxr2 is the target name.
In the future we'll have different targets based on draco board.
All changes are purely non-functional and basically rename dxr2
to draco.

One style fix in board.c that existed already before.

Signed-off-by: Samuel Egli <samuel.egli@siemens.com>
Reviewed-by: Roger Meier <r.meier@siemens.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Wolfgang Denk <wd@denx.de>