clk: mvebu: add Orion5x clock driver

clk: mvebu: add Orion5x clock driver

This commit adds a core clock driver for the Orion5x SoC, with support
for the tclk, the CPU frequency and the DDR frequency. All the details
about the Sample-At-Reset register were extracted from the U-Boot
sources for Orion5x.

Note that Orion5x does not have gatable clocks, so this core clock
driver is sufficient to support clocking on Orion5x platforms.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Link: https://lkml.kernel.org/r/1398202002-28530-5-git-send-email-thomas.petazzoni@free-electrons.com
Cc: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>