[PATCH] drivers/base/: proper prototypes

This patch contains the following changes:
- move prototypes to base.h
- sys.c should #include "base.h" for getting the prototype of it's
  global function system_bus_init()

Note that hidden in this patch there's a bugfix:

Caller and callee disagreed regarding the return type of
sysdev_shutdown().

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>