net: add MMIO Register MDIO MUX driver

Add support for MMIO register MDIO muxes based on the Linux mdio-mux-mmioreg driver.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 0e84c22..41fa2fe 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -790,4 +790,11 @@
 	  This driver supports the MDIO bus found on the Fman 10G Ethernet MACs and
 	  on the mEMAC (which supports both Clauses 22 and 45).
 
+config MDIO_MUX_MMIOREG
+	bool "MDIO MUX accessed as a MMIO register access"
+	depends on DM_MDIO_MUX
+	help
+	  This driver is used for MDIO muxes driven by writing to a register in
+	  the MMIO physical memory.
+
 endif # NETDEVICES