misc/eeprom: add eeprom access driver for digsy_mtc board

Both displays on digsy_mtc board obtain their configuration from microwire
EEPROMs which are connected to the SoC over GPIO lines.  We need an easy
way to access the EEPROMs to write the needed display configuration or to
read out the currently programmed configuration.  The generic
eeprom_93xx46 SPI driver added by previous patch allows EEPROM access over
sysfs.  Using the simple driver added by this patch we provide used GPIO
interface and access control description on the board for generic
eeprom_93xx46 driver and spi_gpio driver.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Jonathan Cameron <jic23@cam.ac.uk>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>