boards: shields: Add nRF70 series EKs (Evaluation kits)

These shields in the Arduino form factor can be mounted on supported
boards and can provide Wi-Fi6 capability.

Base shield is nRF7002, with variants as nRF7001 (2.4GHz only) and
nRF7000 (dual band scan only).

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>