[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>

drivers/mtd/devices/Kconfig

@@ -69,12 +69,21 @@ config MTD_DATAFLASH26
 	  If you have such a board and such a DataFlash, say 'Y'.
 
 config MTD_M25P80
-	tristate "Support for M25 SPI Flash"
+	tristate "Support most SPI Flash chips (AT26DF, M25P, W25X, ...)"
 	depends on SPI_MASTER && EXPERIMENTAL
 	help
-	  This enables access to ST M25P80 and similar SPI flash chips,
-	  used for program and data storage.  Set up your spi devices
-	  with the right board-specific platform data.
+	  This enables access to most modern SPI flash chips, used for
+	  program and data storage.   Series supported include Atmel AT26DF,
+	  Spansion S25SL, SST 25VF, ST M25P, and Winbond W25X.  Other chips
+	  are supported as well.  See the driver source for the current list,
+	  or to add other chips.
+
+	  Note that the original DataFlash chips (AT45 series, not AT26DF),
+	  need an entirely different driver.
+
+	  Set up your spi devices with the right board-specific platform data,
+	  if you want to specify device partitioning or to use a device which
+	  doesn't support the JEDEC ID instruction.
 
 config MTD_SLRAM
 	tristate "Uncached system RAM"