jtag/drivers/ulink: auto-detect OpenULINK USB endpoints numbers

jtag/drivers/ulink: auto-detect OpenULINK USB endpoints numbers

This should provide greater compatibility with different OpenULINK
targets which might be using various endpoints numbers. Since they're
advertised in the USB descriptor anyway it makes sense to autodetect
them.

Interface is no longer claimed before attempting to load firmware to a
freshly booted device, so I have no idea if this will break on windows
or other uncommon systems (Paul).

Change-Id: Iee10dcb6911dcf46239c430e174d9f98b5bde3c2
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2445
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>