drivers: i3c: dw: Add clock subsystem and pinctrl support

Add support for clock subsystem configuration and pinctrl in the
DesignWare I3C driver to enable proper clock control and pin
management on platforms that require them.

Changes include:
- Add clock_subsys field to dw_i3c_config structure.
- Update clock_control_get_rate() and clock_control_on() calls to use
  the configured clock subsystem instead of NULL.
- Use COND_CODE_1 with DT_INST_PHA_HAS_CELL to conditionally extract
  clock subsystem ID from devicetree, providing backward compatibility
  for platforms without clkid cell.
- Include pinctrl-device.yaml in devicetree binding to enable pinctrl
  support for platforms that need pin configuration.
- Gracefully fallback to NULL behavior when clkid is not specified.

This follows the same pattern used by other I3C drivers (mcux, renesas_ra)
and enables proper clock management for SoCs that require clock subsystem
identifiers while maintaining compatibility with existing devicetree
configurations.

Signed-off-by: Shreehari HK <shreehari.hk@alifsemi.com>