iommu/vt-d: Relocate struct/function declarations to its header files

To reuse the static functions and the struct declarations, move them to
corresponding header files and export the needed functions.

Cc: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Gayatri Kammela <gayatri.kammela@intel.com>
Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>