tests: drivers: gpio: gpio_basic_api: add support for gd32vf103v_eval

Add DT overlay to run gpio_basic_api test on GD32VF103V-EVAL board. In
order to make testing easy a couple of accessible pins have been
selected: PD0 and PD1 pins exposed via JP13 and JP4 respectively.

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