Change PciIo::GetBarAttributes() to return unsupported for a unsupported bar even it's below 6 to follow the UEFI Spec.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15538 6f19259b-4bc3-4df7-8a09-765794883524