spi: wpcm-fiu: differentiate between unsupported and invalid requests

spi: wpcm-fiu: differentiate between unsupported and invalid requests

When the requested dirmap accesses are outside of the window, it is
probably more sensible to return -EINVAL rather than an "unsupported"
error code. If however the operation in itself is not supported, then
-EOPNOTSUP is likely going to be preferred as it is a standard error
code.

>From a caller (and reviewer) point of view, distinguising between the
two may be helpful because somehow one can be "fixed" while the other
will always be refused no matter how hard we try.

As part of a wider work to bring spi-nand continuous reads, it was
useful to easily catch the upper limit direct mapping boundaries for
each controller, with the idea of enlarging this area from a page to an
eraseblock, without risking too many regressions.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://msgid.link/r/20240522145255.995778-5-miquel.raynal@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>