drm: zynq_drm: vtc: Set polarity/source config in config_sig()

Polarity/source configurations are done when the signal is configured.
Those were originally set in probe() which disappeared after reset().

Signed-off-by: hyun woo kwon <hyunk@xilinx.com>
drm: zynq_drm: encoder: Change the order of set si570 freq

Set the si570 frequency after vtc is set. This fixes the 'imprecise abort'
which is generated when the vtc register is read in vtc_config_sig()

Signed-off-by: hyun woo kwon <hyunk@xilinx.com>