ARM: mm: cleanup checks for membank overlap with vmalloc area
On Keystone platforms, physical memory is entirely outside the 32-bit
addressible range. Therefore, the (bank->start > ULONG_MAX) check below marks
the entire system memory as highmem, and this causes unpleasentness all over.
This patch eliminates the extra bank start check (against ULONG_MAX) by
checking bank->start against the physical address corresponding to vmalloc_min
instead.
In the process, this patch also cleans up parts of the highmem sanity check
code by removing what has now become a redundant check for banks that entirely
overlap with the vmalloc range.