spi: dw: differentiate between unsupported and invalid requests

The driver does not support dirmap write operations, return -EOPTNOTSUPP
in this case.

Most controllers have a maximum linear mapping area. Requests beyond
this limit can be considered invalid, rather than unsupported.

>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 <[email protected]>
Link: https://msgid.link/r/[email protected]
Signed-off-by: Mark Brown <[email protected]>

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