net: ipa: flag duplicate memory regions

Add a test in ipa_mem_valid() to ensure no memory region is defined
more than once, using a bitmap to record each defined memory region.
Skip over undefined regions when checking (we can have any number of
those).

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>