drivers: timer: Add ULPT timer for power management on Renesas RA MCUs

drivers:
- Added ULPT timer driver in `renesas_ra_ulpt_timer.c`.
- Updated `clock_control_renesas_ra_cgc.c` for ULPT clock settings.
- Updated `uart_renesas_ra8_sci_b.c` for power management support.
- Updated `CMakeLists.txt` and `Kconfig` to integrate ULPT timer.
- Added `Kconfig.renesas_ra_ulpt` for ULPT-specific configurations.

dts bindings:
- Added `renesas,ra-ulpt.yaml` for ULPT node bindings.
- Added `renesas,ra-ulpt-timer.yaml` for ULPT timer bindings.

modules:
- Updated `Kconfig.renesas_fsp` to support ULPT and LPM.

Signed-off-by: Khanh Nguyen <khanh.nguyen.wz@bp.renesas.com>