mtd: rawnand: nandsim: Use a consistent ns_ prefix for all functions

Some functions are prefixed "nandsim_", others "ns_" and many are
simply not prefixed at all. Make this file consistent by prefixing all
functions by "ns_".

This is a mechanical change. Sometimes the line is a bit reworked as
well to fit the kernel coding style. For instance, there are several
places where displayed strings are cut. When one of this line is
changed because of the naming update, the two parts of the strings
gets concatenated.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200525085851.17682-4-miquel.raynal@bootlin.com