MdePkg: Handle AcpiExp device path when optional para is not specified

MdePkg: Handle AcpiExp device path when optional para is not specified

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1243

AcpiExp text device path: AcpiExp(HID,CID,UIDSTR)
And according to UEFI spec, the CID parameter is optional
and has a default value of 0. But current implementation
miss to check following cases for the AcpiExp.
FromText:when text device is AcpiExp(HID,,UIDSTR)/AcpiExp(HID,0,UIDSTR)
ToText: when the CID is 0 in the node structure

This commit is to do the enhancement.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>