1) Add type casting for argument "a" in EFI_ERROR(a), since if compare two constants...

1) Add type casting for argument "a" in EFI_ERROR(a), since if compare two constants without specify data type, compiler maybe could not understand what is the actual data type of constant. The default would treat it as unsigned data. therefore, if the argument a of EFI_ERROR(a) is constant, for instance the EFI_LOAD_ERROR, the EFI_ERROR(a) would always be FALSE.
2) Remove PcdDriverPcdLibNull.
3) Add more ASSERT() in BasePcdLibNull to detect the incorrect usage of Pcd Library.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@3643 6f19259b-4bc3-4df7-8a09-765794883524