nulink: add minimal support for Nu-Link2

nulink: add minimal support for Nu-Link2

Implementation largely taken from Nuvoton github
	https://github.com/OpenNuvoton/OpenOCD-Nuvoton

Reset is still not fully compatible with OpenOCD framework.
Adapted to hidapi.

Change-Id: Ieb1791b1b7f0b444c15c9668f8f2bcf34975d48f
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Signed-off-by: Zale Yu <cyyu@nuvoton.com>
Reviewed-on: http://openocd.zylin.com/5720
Tested-by: jenkins
Reviewed-by: Saravanan Sekar <saravanan@linumiz.com>
Reviewed-by: Marc Schink <dev@zapb.de>