clk: mvebu: introduce per-clock-gate flags

Clock gates found on MVEBU SoCs get registered by a common function.
To allow specific SoCs to provide tweaks introduce flags to the clock
gate descriptor instead of filling up the common function SoC specific
tweaks.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>