dw3000: keep coex gpio high during entire ranging round

The WiFi coex GPIO is put high and down for RX/TX operation.

But it is supposed to stay high for the entire ranging round duration.

The `need_ranging_clock` and delay before next operation is used to change
this behavior.

closes UWB-1496

Bug: 171489641
Change-Id: I8fe2bfdb460aa12105280600f177d8c39897da65
Signed-off-by: Jean-Michel RIOT <jean-michel.riot@qorvo.com>