ARMV7: OMAP3: Add expansion board detection for Overo

Overo expansion boards contain an i2c eeprom to identify themselves.
This patch adds code to read and parse the eeprom contents.  It prints
the expansion board name and revision and modifies environment variables
as appropriate.

Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>