ARM: multi_v7_defconfig: add NXP FlexCAN IP support

Enable FlexCAN support as module by default. FlexCAN can be found
on various NXP designs such as the i.MX and Vybrid SoC family.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>