spi: make `cs_change_delay` the first user of the `spi_delay` logic

Since the logic for `spi_delay` struct + `spi_delay_exec()` has been copied
from the `cs_change_delay` logic, it's natural to make this delay, the
first user.

The `cs_change_delay` logic requires that the default remain 10 uS, in case
it is unspecified/unconfigured. So, there is some special handling needed
to do that.

The ADIS library is one of the few users of the new `cs_change_delay`
parameter for an spi_transfer.

The introduction of the `spi_delay` struct, requires that the users of of
`cs_change_delay` get an update. This change also updates the ADIS library.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20190926105147.7839-4-alexandru.ardelean@analog.com
Signed-off-by: Mark Brown <broonie@kernel.org>