Add support for burning flash on lpc4337.
adiv5_swdp: allow to connect to a sleeping target by pulling SRST

This patch introduces a new command, "connect_srst [enable|disable]"
which allows to enable special mode in which SRST would be pulled low
before the SWD scan till attaching to a target.

Since on Cortex-Mx the SRST signal doesn't gate JTAG and SWD, it's
possible to connect to a target while holding reset, ask it to stop at
reset vector and only then deassert reset, thus allowing to attach to
the kind of firmware that goes immediately to sleep or disables
debugging by other means early on start.

Tested on an STM32VLDiscovery board with STM32F100 configured to go to
STOP mode and executing WFI in the very beginning of main().

Signed-off-by: Paul Fertser <fercerpav@gmail.com>
stlink: add support for SRST handling

This enables SRST signals in open drain mode for both stlinkv1 and
stlinkv2 hardware platforms.

Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Add support for Atmel SAM3N devices.