ssb: add Kconfig entry for compiling SoC related code

This allows saving a little of space when not using ssb on Broadcom SoC.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
diff --git a/drivers/ssb/main.c b/drivers/ssb/main.c
index bea823e..5d1e9a0 100644
--- a/drivers/ssb/main.c
+++ b/drivers/ssb/main.c
@@ -761,6 +761,7 @@
 EXPORT_SYMBOL(ssb_bus_sdiobus_register);
 #endif /* CONFIG_SSB_PCMCIAHOST */
 
+#ifdef CONFIG_SSB_HOST_SOC
 int ssb_bus_ssbbus_register(struct ssb_bus *bus, unsigned long baseaddr,
 			    ssb_invariants_func_t get_invariants)
 {
@@ -777,6 +778,7 @@
 
 	return err;
 }
+#endif
 
 int __ssb_driver_register(struct ssb_driver *drv, struct module *owner)
 {