drivers: mux: mmio-based syscon mux controller

This adds a driver for mmio-based syscon multiplexers controlled by
bitfields in a syscon register range.
This is heavily based on the linux mmio-mux driver.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
index 35c1c56..f15ee4f 100644
--- a/drivers/mux/Kconfig
+++ b/drivers/mux/Kconfig
@@ -8,4 +8,18 @@
 	 controllers. It provides the same API as Linux and mux drivers should
 	 be portable with a minimum effort.
 
+if MULTIPLEXER
+
+config MUX_MMIO
+	bool "MMIO register bitfield-controlled Multiplexer"
+	depends on MULTIPLEXER && SYSCON
+	help
+	  MMIO register bitfield-controlled Multiplexer controller.
+
+	  The driver builds multiplexer controllers for bitfields in a syscon
+	  register. For N bit wide bitfields, there will be 2^N possible
+	  multiplexer states.
+
+endif
+
 endmenu