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/Kconfig b/drivers/clk/Kconfig
index 60a6859..edb4ca5 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -88,6 +88,7 @@
 source "drivers/clk/exynos/Kconfig"
 source "drivers/clk/at91/Kconfig"
 source "drivers/clk/renesas/Kconfig"
+source "drivers/clk/mvebu/Kconfig"
 
 config ICS8N3QV01
 	bool "Enable ICS8N3QV01 VCXO driver"