MdePkg: CI: Add PrEval entry

Adds a PrEval entry to the package's ci.yaml file which is used to
verify if the package uses a particular library instance when that
library instance file (INF) is updated.

When a library instance file (INF) is updated, PrEval will review each
package's DSC as described in the ci.yaml file to determine if the
package uses said library instance. If the package does use the library
instance, it will be built and tested to ensure the package is not
broken from the change.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Signed-off-by: Joey Vagedes <joeyvagedes@gmail.com>

Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>

MdePkg/MdePkg.ci.yaml

@@ -9,6 +9,9 @@
 # SPDX-License-Identifier: BSD-2-Clause-Patent
 ##
 {
+    "PrEval": {
+        "DscPath": "MdePkg.dsc",
+    },
     ## options defined .pytool/Plugin/LicenseCheck
     "LicenseCheck": {
         "IgnoreFiles": [