ARM: bcm_defconfig: CONFIG_OABI_COMPAT default off

Now that CONFIG_OABI_COMPAT is off by default, remove the explicit
disabling of this feature.

Signed-off-by: Tim Kryger <tim.kryger@linaro.org>
Reviewed-by: Markus Mayer <markus.mayer@linaro.org>
Signed-off-by: Christian Daudt <bcm@fixthebug.org>