ARM: omap: move omap_get_config et al. to .init.text

All callers of these functions live in .init.text, so these can go there,
too.  There they must not be exported anymore, this is no problem though,
as all callers are always built-in.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>