dt: bindings: dma: xilinx: dpdma: Remove unused properties

dt: bindings: dma: xilinx: dpdma: Remove unused properties

This removes a couple of unused / incorrect DT properties.
Number of dma-chnnels is fixed in the IPs. No need to be a DT property,
and the driver doesn't use it.
The clock rate is a runtime configuration, which comes through
CCF APIs at runtime. Also, the driver doesn't need to set it to any
specific frequency. It's set by the system level configuration.

Signed-off-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>