mux: Makefile: Add config for mux drivers

Add config required to build mmio-mux driver and dependencies.

Signed-off-by: Anurag Dutta <a-dutta@ti.com>
diff --git a/drivers/Makefile b/drivers/Makefile
index 9440af1..0e1f58c 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -21,6 +21,7 @@
 obj-$(CONFIG_$(PHASE_)LED) += led/
 obj-$(CONFIG_$(PHASE_)MMC) += mmc/
 obj-y += mtd/
+obj-$(CONFIG_MULTIPLEXER) += mux/
 obj-$(CONFIG_$(PHASE_)ETH) += net/
 obj-$(CONFIG_$(PHASE_)PCH) += pch/
 obj-$(CONFIG_$(PHASE_)PCI) += pci/