dts: nxp: move nxp,imx-gpt.yaml to the counter folder

- Moves nxp,imx-gpt.yaml from the timer to the counter folder,
  as this is the binding for the counter driver
  drivers/counter/counter_mcux_gpt.c
- Fixes: #100947

Signed-off-by: Andrej Butok <andrey.butok@nxp.com>