spi: differentiate between unsupported and invalid

spi: differentiate between unsupported and invalid

Merge series from Miquel Raynal <miquel.raynal@bootlin.com>:

I am working on spi-nand continuous read support, which lead me to check
what spi controllers were capable of.

>From a caller (and reviewer) point of view, distinguishing between error
cases has been proven useful, especially between two conditions:
- the request is totally unsupported and will never work
- the request is typically out of range somehow but a subsequent call
  with corrected parameters might work

So while I was statically reading the various drivers, I attempted to
clarify these situations and thought it might be nice to have this
upstream as well.

As ENOTSUPP is not a SUSV4 code and previous series have already been
merged to reduce its use, I also converted these few cases to EOPNOTSUP
instead, but if anybody doesn't like these changes, it can be dropped.