ARM: defconfig: Update multi_v7 to use PREEMPT

Using CONFIG_PREEMPT as preemption model for ARMv7 systems
appear to be the most reasonable default.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm/configs/multi_v7_defconfig

 CONFIG_SYSVIPC=y
 CONFIG_NO_HZ=y
 CONFIG_HIGH_RES_TIMERS=y
+CONFIG_PREEMPT=y
 CONFIG_CGROUPS=y
 CONFIG_BLK_DEV_INITRD=y
 CONFIG_EMBEDDED=y