Fix some minor bugs on PCD schema according to final schema email send by Larry

Fix some minor bugs on PCD schema according to final schema email send by Larry
1) In <PcdData> of <PcdBuildDefinition>, MaxDatumSize should be added;
2) In <PcdData> of <PcdBuildDefinition>, the number of <Value> should be [0..1] but not [0..n];
3) The max occurs of <SkuId> in <DynamicPcdBuildDefinitions> should be 1;

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@470 6f19259b-4bc3-4df7-8a09-765794883524