ARM: OMAP: omap_common_late_init may be unused

Some OMAP SoCs use this function while others do not, and that
causes a warning when building multi_v7_defconfig. Marking the
function __maybe_unused silences the harmless warning without the
need to add complex #ifdef logic.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Tony Lindgren <tony@atomide.com>