OvmfPkg: move VirtioBlkDxe/Virtio.h to Include/IndustryStandard/Virtio.h

OvmfPkg: move VirtioBlkDxe/Virtio.h to Include/IndustryStandard/Virtio.h

This commit consists of:
- a verbatim move ("similarity index 100%" in git parlance),
- an updated #include directive in VirtioBlkDxe/VirtioBlk.h,
- and an OvmfPkg.dec package entry in VirtioBlkDxe/VirtioBlk.inf, so that
  the new include directory is searched.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13836 6f19259b-4bc3-4df7-8a09-765794883524