mtd: m25p80: bind to "nor-jedec" ID, for auto-detection

Use the new 'nor-jedec' binding to provide automatic detection of flash
that use the 0x9F READ ID opcode. This can help for use cases where
platforms just specify compatibility with "m25p80", and then see
messages like this:

  m25p80 spi32766.0: found s25fl256s1, expected m25p80

Instead, they can just specify the generic string and see this:

  m25p80 spi32766.0: s25fl256s1 (32768 Kbytes)

Also, update the language about m25p_ids[] to straighten out the
expectations here. We should no longer need to continuously grow the
m25p_ids[] table, and in fact, we might want to start removing entries
which are not used in device trees so far, so we can just default to
auto-detection as much as possible in the future.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Rafał Miłecki <zajec5@gmail.com>