[PATCH] SPI eeprom driver

This is adds a simple SPI EEPROM driver, providing access to the EEPROM
through sysfs much like the I2C "eeprom" driver ...  except this driver
supports write access, and multiple EEPROM sizes.

From: "Tuppa, Walter" <walter.tuppa@siemens.com>

Since I have EEPROMs on SPI with different address sizing, I made some
changes to your at25.c to support them.  Works perfectly.  (Also includes a
small bugfix for the "what size address" test.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Walter Tuppa <walter.tuppa@siemens.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>