mtd: spinand: Add an optional frequency to read from cache macros

While the SPINAND_PAGE_READ_FROM_CACHE_FAST_OP macro is supposed to be
able to run at the flash highest supported frequency, it is not the case
of the regular read from cache, which may be limited in terms of maximum
frequency. Add an optional argument to this macro, which will be used to
set the maximum frequency, if any.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>