Revert "staging: fsl-mc: delete prototype of unimplemented function"

This reverts commit be6faff7.

The whole series is broken, so back it all out.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Cc: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fsl-mc/include/mc-bus.h

@@ -91,6 +91,8 @@ void fsl_mc_init_all_resource_pools(struct fsl_mc_device *mc_bus_dev);
 
 void fsl_mc_cleanup_all_resource_pools(struct fsl_mc_device *mc_bus_dev);
 
+bool fsl_mc_bus_exists(void);
+
 void fsl_mc_get_root_dprc(struct device *dev,
 			  struct device **root_dprc_dev);