setup.c unconditionally sets the sys-led mode (blinking rate) to a
permanent high output. This may cause issues when a board expects this
pin to toggle periodically, e.g. when hooked up to an external watchdog.
If the sys-led peripheral is used to control an LED, the mux should be
configured to use the pin as GPIO0, allowing for better control as a
GPIO LED.
Signed-off-by: Sander Vanheule <sander@svanheule.net>