package: add openocd support

with only the following Adapters
 - FTDI FT2xxx/FT4xxx
 - J-Link (Segger and Atmel SAM-ICE)
 - Versaloon-Link JTAG Adapter

[Peter: Config.in tweaks]
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Patrice Vilchez <patrice.vilchez@atmel.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>