Add the memory management code from uVisor to a shared location that is
suitable for both supported and unsupported use. To do this, we copy all
the RTX-specific files from the RTX folders in uVisor.
Note that the page allocator code is so identical between uVisor supported
and unsupported mode that we can copy the file as-is from uVisor for use on
unsupported targets. This commit performs that copying, to a file called
page_allocator.c_inc, which is included from unsupported_page_allocator.c
only for targets where uVisor is not present.