ArmPkg/ArmMmuLib: Explicitly cast UINT32 data conversions
    
    REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2835
    
    There's several occurrences of a UINT64 or an EFI_PHYSICAL_ADDRESS
    being assigned to a UINT32 value in ArmMmuLib. These result in
    warning C4244 in VS2019:
    
    warning C4244: '=': conversion from 'UINT64' to 'UINT32', possible
    loss of data
    
    warning C4244: '=': conversion from 'EFI_PHYSICAL_ADDRESS' to
    'UINT32', possible loss of data
    
    This change explicitly casts the values to UINT32.
    
    These can be reproduced with the following build command:
    build -b DEBUG -a ARM -t VS2019 -p ArmPkg/ArmPkg.dsc
    -m ArmPkg/Library/ArmMmuLib/ArmMmuBaseLib.inf
    
    Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
    Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>