aice: add Andes AICE support

Andes AICE uses USB to transfer packets between OpenOCD and AICE.
It uses high-level USB commands to control targets instead of using
JTAG signals. I define an interface as aice_port_api_s. It contains
all basic operations needed by target-dependent code.

Change-Id: I117bc4f938fab2732e44c509ea68b30172d6fdb9
Signed-off-by: Hsiangkai Wang <hsiangkai@gmail.com>
Reviewed-on: http://openocd.zylin.com/1256


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>