Without that gcc 7.3.1 (from OSELAS.Toolchain-2018.02.0) makes
mvebu_remap_registers a standalone function which in its prolog saves
two registers to the stack. However this function is called early during
startup when there is no stack available yet and sp still points into
the nirvana which makes barebox crash.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>