ArmPkg/CpuDxe: ignore attribute changes during SyncCacheConfig()
To prevent the initial MMU->GCD memory space map synchronization from
stripping permissions attributes [which we cannot use in the GCD memory
space map, unfortunately], implement the same approach as x86, and ignore
SetMemoryAttributes() calls during the time SyncCacheConfig() is in
progress. This is a horrible hack, but is currently the only way we can
implement strict permissions on arbitrary memory regions [as opposed to
PE/COFF text/data sections only]