board: ns3: default reset type to L3

Default "reset" from U-Boot to L3 reset.
"reset" command with argument will trigger L1 reset.

Signed-off-by: Rajesh Ravi <rajesh.ravi@broadcom.com>
Signed-off-by: Bharat Kumar Reddy Gooty <bharat.gooty@broadcom.com>
Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Reviewed-by: Simon Glass <sjg@chromium.org>