ARMV7: OMAP3: IGEP: Rename TEXT_BASE

Commit 14d0a02a "Rename TEXT_BASE into CONFIG_SYS_TEXT_BASE" missed the
IGEP boards since they were just added.

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