jtag/drivers/openjtag: Add support for Cypress CY7C65215

jtag/drivers/openjtag: Add support for Cypress CY7C65215

The Cypress CY7C65215 Dual Channel USB-Serial Bridge Controller [1]
understands the OpenJTAG protocol over a proprietary USB interface.

This patch adds support for the CY7C65215 to the openjtag interface
driver.  A new configuration option, `openjtag_variant`, allows to
select the transport to use.

Libusb (1.x or 0.1) is now a hard dependency of the openjtag driver.
This should not be a big issue as libftdi also depends on it.

[1] http://www.cypress.com/?rID=82870

Change-Id: I55ffb3fd9e006eb311e405d9fb836bb119644bfd
Signed-off-by: Vianney le Clément de Saint-Marcq <vianney.leclement@essensium.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Reviewed-on: http://openocd.zylin.com/2805
Tested-by: jenkins
Reviewed-by: Jiri Kastner <cz172638@gmail.com>
Reviewed-by: Paul Fertser <fercerpav@gmail.com>