A previous commit 3a9d948032e27f690e1fb09084c36bd47b1a75a0 can cause
lock-ups of the RMT driver, so this commit reverses that, adds a loop_en
flag, and explicitly controls the TX interrupt in write_pulses(). This
provides correct looping, non-blocking writes and sensible behaviour for
wait_done().
See also #6167.
7dbef5377c