iommu/mediatek: Fix a build warning of BIT(32) in ARM

The commit ("iommu/mediatek: Enlarge the validate PA range
for 4GB mode") introduce the following build warning while ARCH=arm:

   drivers/iommu/mtk_iommu.c: In function 'mtk_iommu_iova_to_phys':
   include/linux/bitops.h:6:24: warning: left shift count >= width
of type [-Wshift-count-overflow]
    #define BIT(nr)   (1UL << (nr))
                           ^
>> drivers/iommu/mtk_iommu.c:407:9: note: in expansion of macro 'BIT'
      pa |= BIT(32);

  drivers/iommu/mtk_iommu.c: In function 'mtk_iommu_probe':
   include/linux/bitops.h:6:24: warning: left shift count >= width
of type [-Wshift-count-overflow]
    #define BIT(nr)   (1UL << (nr))
                           ^
   drivers/iommu/mtk_iommu.c:589:35: note: in expansion of macro 'BIT'
     data->enable_4GB = !!(max_pfn > (BIT(32) >> PAGE_SHIFT));

Use BIT_ULL instead of BIT.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>