ARM: bcm2835: enable V6K instead of plain V6

The bcm2835 is an ARM1176 which has all the V6K extensions except for SMP,
so V6K should be selected instead. Dropping the select will use
the default for ARCH_MULTI_V6 which is V6K.

Signed-off-by: Rob Herring <robh@kernel.org>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>