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

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

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

Sata device path format:Sata(HPN, PMPN, LUN)
According to UEFI Spec, the PMPN is an integer between
0 and 65535 and is optional. If not provided, the default is 0xFFFF.

This commit is to do the enhancement for Sata device path
when optional para is not specified.

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>