ARM: vt8500: enable V6K instead of plain V6

The wm8750 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>
Cc: Tony Prisk <linux@prisktech.co.nz>