[MTD] m25p80 handles more chips, uses JEDEC ids and small eraseblocks

Update chip ID tables in m25p80 to handle more SPI flash chips, matching
datasheets.  All of these can use the same core operations and are newer
chips that support the JEDEC "read id" instruction:

 - Atmel AT25 and AT26 (seven chips)
 - Spansion S25SL (five chips)
 - SST 25VF (four chips)
 - ST M25, M45 (five more chips)
 - Winbond W25X series (seven chips)

That JEDEC instruction is now used, either to support a sanity check on the
platform data holding board configuration data, or to determine chip type
when it's not included in platform data.  In fact, boards that don't need a
standard partition table may not need that platform data any more.

For chips that support 4KiB erase units, use that smaller block size instead
of the larger size (usually 64KiB); it's less wasteful.  (Tested on W25X80.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>