jtag: drivers: xlnx-pcie-xvc: fix build after merge

jtag: drivers: xlnx-pcie-xvc: fix build after merge

Commit [1] was submitted in gerrit well before the conflicting
commit [2] get merged in master branch. While it was fine
committing in master branch [1] alone, it should not be
committed "as is" after [2].
Unfortunately gerrit did not complained committing [1] after [2].
The result is that master branch does not build anymore when the
driver xlnx-pcie-xvc is enabled at configure time by the optional
flag --enable-xlnx-pcie-xvc.

Apply to the driver the required changes as in [2].
While there, remove the duplicated struct xlnx_pcie_xvc_transports
and the struct field already implicitly initialized to zero.

[1] ff6d0704ecd6 ("jtag: drivers: xlnx-pcie-xvc: Add support for
    Xilinx XVC/PCIe")
[2] efd1d642220a ("adapter: switch from struct jtag_interface to
    adapter_driver")

Change-Id: I5498479b802a231afbee1b845ae9775e1da7c728
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5402
Reviewed-by: Moritz Fischer <moritzf@google.com>
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>