driver: clk: Add support for clocks on Armada 37xx

The drivers are based on Linux driver by Gregory Clement.

The TBG clocks support only the .get_rate method.
  - since setting rate is not supported, the driver computes the rates
    when probing and so subsequent calls to the .get_rate method do not
    read the corresponding registers again

The peripheral clocks support methods .get_rate, .enable and .disable.

  - the .set_parent method theoretically could be supported on some clocks
    (the parent would have to be one of the TBG clocks)

  - the .set_rate method would have to try all the divider values to find
    the best approximation of a given rate, and it doesn't seem like
    this should be needed in U-Boot, therefore not implemented

Signed-off-by: Marek Behun <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/drivers/clk/mvebu/Kconfig b/drivers/clk/mvebu/Kconfig
new file mode 100644
index 0000000..e776a15
--- /dev/null
+++ b/drivers/clk/mvebu/Kconfig
@@ -0,0 +1,11 @@
+config CLK_MVEBU
+	bool "MVEBU clock drivers"
+	depends on CLK && ARCH_MVEBU
+	help
+	  Enable support for clock present on Marvell MVEBU SoCs.
+
+config CLK_ARMADA_3720
+	bool "Marvell Armada 3720 clock driver"
+	depends on CLK_MVEBU && ARM64
+	help
+	  Enable this to support the clocks on Marvell Armada 3720 SoC.