Do not export am43xx_control_{save,restore}_context to avoid
the foloowing warnings:

arch/arm/mach-omap2/control.c:687:6: warning: symbol 'am43xx_control_save_context' was not declared. Should it be static?
arch/arm/mach-omap2/control.c:701:6: warning: symbol 'am43xx_control_restore_context' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>