Currently, any range passed to CpuArchProtocol::SetMemoryAttributes is
fully broken down into page mappings if the start or the size of the
region happens to be misaliged relative to the section size of 1 MB.
This is going to result in memory being wasted on second level page tables
when we enable strict memory permissions, given that we remap the entire
RAM space non-executable (modulo the code bits) when the CpuArchProtocol
is installed.
So refactor the code to iterate over the range in a way that ensures
that all naturally aligned section sized subregions are not broken up.