ARM: DRA7/AM43XX: fix header definition for omap44xx_restart

omap44xx_restart is defined as a static void inline when DRA7/AM437X is
defined alone, which implies that the restart function is no longer
functional even though it is built in. So, fix the definition of the
same.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>