OvmfPkg: Add basic skeleton for the XenBus bus driver.

OvmfPkg: Add basic skeleton for the XenBus bus driver.

This includes Component Name and Driver Binding.

Change in V4:
- Replace the license by the commonly used file header text.
- Add brief description for the driver.

Change in V3:
- enable compilation for Ia32 and Ia32X64
- fix version (driver binding)

Change in V2:
- Simple support of controller name.
- Cleaning up comments, files header.
- Add Licenses
- Rename XenbusDxe to XenBusDxe.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16258 6f19259b-4bc3-4df7-8a09-765794883524