soundwire: cadence: add parity error injection through debugfs

The Cadence IP can inject errors, let's make use of this capability to
test Slave parity error checks.

See e.g. example log where both the master and slave detect the parity
error injected on a dummy read command.

cd /sys/kernel/debug/soundwire/master-1/intel-sdw/
echo 1 > cdns-parity-error-injection

[   44.756249] intel-master sdw-master-1: Parity error
[   44.756313] intel-master sdw-master-1: Msg NACK received
[   44.756366] intel-master sdw-master-1: Msg NACKed for Slave 15
[   44.756375] intel-master sdw-master-1: trf on Slave 15 failed:-5
[   44.756382] intel-master sdw-master-1: parity error injection, read: -5
[   44.756649] rt1308 sdw:1:25d:1308:0: Parity error detected

The code makes sure the Master device is resumed, hence the clock
restarted, before sending a parity error.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Link: https://lore.kernel.org/r/20200908134521.6781-8-yung-chuan.liao@linux.intel.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>