scripts: west: Add reset-after-load argument to jlink runner

Adds a new argument to the jlink runner to reset the device after
loading code to flash. This fixes a problem with the lpcxpresso54114
board where it was necessary to manually reset the board to get new code
to start running after the 'ninja flash' command. This new argument is
optional and false by default because there are some cases were we must
not reset after load, such as when we load the application into ITCM on
imx rt devices.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>