dts: arm: nordic: nrf5340: adjust OSCILLATORS IP description

- Create a new compatible: nordic,nrf53x-oscillators, as other series,
  e.g. nRF54LX contain a similar but different IP (with PLL control,
  etc.)
- Adjust DT: use recommended node name, remove redundant status okay.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>