iommu/vt-d: Change dmar_ats_supported() to return boolean

iommu/vt-d: Change dmar_ats_supported() to return boolean

According to "Function return values and names" in coding-style.rst, the
dmar_ats_supported() function should return a boolean instead of an
integer. Also, rename "ret" to "supported" to be more straightforward.

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Link: https://lore.kernel.org/r/20250509140021.4029303-3-wei.w.wang@intel.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>