ARM: bcm2835_defconfig: Enable Mini UART console support

Since pl011 is connected to the BT chip, we need to enable the Mini
UART for serial console.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Eric Anholt <eric@anholt.net>