ARM: shmobile: add function declarations for sh7372 DT helper functions

sh7372_add_early_devices_dt() and sh7372_add_standard_devices_dt() are
defined as global functions in arch/arm/mach-shmobile/setup-sh7372.c,
but their declarations are missing. Add them to common.h, where similar
functions for this and other SoC types are already declared.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Simon Horman <horms@verge.net.au>