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

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>

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