Add support for querying the clock domains of the clock pins for the
axi_dmac controller. This allows the core to automatically figure out
whether its different parts run in different clock domains or not and setup
the configuration parameters accordingly.
Being able to auto-detect those configuration parameters makes the core
easier to use and also avoids accidental misconfiguration.
It is still possible to automatically overwrite the configuration
parameters by hand if necessary.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>