hw/arm/smmuv3: Fix potential integer overflow (CID 1432363)

Use the BIT_ULL() macro to ensure we use 64-bit arithmetic.
This fixes the following Coverity issue (OVERFLOW_BEFORE_WIDEN):

  CID 1432363 (#1 of 1): Unintentional integer overflow:

  overflow_before_widen:
    Potentially overflowing expression 1 << scale with type int
    (32 bits, signed) is evaluated using 32-bit arithmetic, and
    then used in a context that expects an expression of type
    hwaddr (64 bits, unsigned).

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Eric Auger <eric.auger@redhat.com>
Message-id: 20201030144617.1535064-1-philmd@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>