fsi: master-gpio: Add more tracepoints

This adds a few more tracepoints that have proven useful when
debugging issues with the FSI bus.

This also makes echo_delay() use clock_zeros() instead of
open-code it in order to share the tracepoint.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>