MAINTAINERS: Update for INTEL IOMMU (VT-d) entry

Update the INTEL IOMMU (VT-d) entry and add myself as the
co-maintainer. I have several years of VT-d development
experience and have actively contributed to Intel VT-d
driver during recent two years. I volunteer to take this
rule. With this role, I can better help review and test
patches.

Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>