xilinx: drivers: Use '_' instead of '-' in driver name

xilinx: drivers: Use '_' instead of '-' in driver name

The most of drivers are using '_' instead of '-' in driver name. That's why
sync up these names to be aligned. It looks quite bad to see both in use.
It is visible via dm tree command.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>