drivers: sensor: Add sensor clock API support

This commit introduces a new Sensor Clock API, enabling the retrieval
of cycle counts and conversion to nanoseconds based on the system or
external clock. The API includes:

- `sensor_clock_get_cycles()` to get the current cycle count from the
  sensor clock.
- `sensor_clock_cycles_to_ns()` to convert cycles to nanoseconds using
  the clock's frequency.

The implementation supports both system clocks and external clocks
defined in the device tree, making the sensor clock integration more
flexible for various sensor use cases.

Signed-off-by: Mark Chen <mark.chen@cienet.com>