iommu/vt-d: Correctly check format of page table in debugfs

PASID support and enable bit in the context entry isn't the right
indicator for the type of tables (legacy or scalable mode). Check
the DMA_RTADDR_SMT bit in the root context pointer instead.

Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Sai Praneeth <sai.praneeth.prakhya@intel.com>
Fixes: dd5142ca ("iommu/vt-d: Add debugfs support to show scalable mode DMAR table internals")
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>