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/Makefile b/drivers/ssb/Makefile
index 30194c5..64a0968 100644
--- a/drivers/ssb/Makefile
+++ b/drivers/ssb/Makefile
@@ -7,7 +7,7 @@
 ssb-$(CONFIG_SSB_PCIHOST)		+= pci.o pcihost_wrapper.o
 ssb-$(CONFIG_SSB_PCMCIAHOST)		+= pcmcia.o bridge_pcmcia_80211.o
 ssb-$(CONFIG_SSB_SDIOHOST)		+= sdio.o
-ssb-y					+= host_soc.o
+ssb-$(CONFIG_SSB_HOST_SOC)		+= host_soc.o
 
 # built-in drivers
 ssb-y					+= driver_chipcommon.o