ARMV7: OMAP3: Fix preprocessor check for CONFIG_OMAP34XX

CONFIG_OMAP34XX must be checked for existence, not value.

Signed-off-by: Luca Ceresoli <luca.ceresoli@comelit.it>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Albert Aribaud <albert.aribaud@free.fr>
Cc: Sandeep Paulraj <s-paulraj@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>