iio: ping: add parallax ping sensors

Add support for parallax ping and laser ping sensors with just one pin
for trigger and echo signal.

This driver is based on srf04. In contrast to it it's necessary to
change direction of the pin and to request the irq just for the period
when the echo is rising and falling. Because this adds a lot of cases
there is this individual driver for handling this type of sensors.

Add a new configuration variable CONFIG_PING to Kconfig and Makefile.

Julia reported an issue with failing to unlock a mutex in some error
paths.

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>