Define board_quiesce_devices() in a shared location

This undocumented function relies on arch-specific code to declare a nop
weak version. Add the weak function in common code instead to avoid having
to duplicate the same function in each arch.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/arm/include/asm/u-boot-arm.h

@@ -37,7 +37,6 @@ int	arch_early_init_r(void);
 
 /* board/.../... */
 int	board_init(void);
-void	board_quiesce_devices(void);
 
 /* cpu/.../interrupt.c */
 int	arch_interrupt_init	(void);