ARMV7: OMAP3: Add expansion board detection for Beagle

Beagle 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. This patch is based on the Overo expansion board code.

Signed-off-by: Koen Kooi <k-kooi@ti.com>
Signed-off-by: Steve Sakoman <steve.sakoman@linaro.org>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>