spi: Catch improper use of PTP system timestamping API

We can catch whether the SPI controller has declared it can take care of
software timestamping transfers, but didn't. So do it.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20191227012444.1204-1-olteanv@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>