ARM: mxs: fix machines' initializers order

Initializers of m28evk and stmp378x_devb fixed to be in order
they are called.

reference: http://article.gmane.org/gmane.linux.ports.arm.omap/50721



Cc: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Lauri Hintsala <lauri.hintsala@bluegiga.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>