jlink: Adjust log verbosity of libjaylink

jlink: Adjust log verbosity of libjaylink

Currently, the log verbosity of libjaylink is not accessible from the
user interface. Therefore, changing the log verbosity of libjaylink is
only possible from within the J-Link driver source code which is not
acceptable for end users.

Output the libjaylink log messages through the logging module of
OpenOCD rather than directly to stderr.

Change-Id: I6bf7bf8f4c8a12fb9e955eeced68224545fa0b5c
Signed-off-by: Marc Schink <openocd-dev@marcschink.de>
Reviewed-on: http://openocd.zylin.com/3701
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>