net: ipa: don't define empty memory regions

The AP_HEADER memory region for both the SDM845 and SC7180 SoCs has
zero size, and has no canaries.  Defining an offset for such a
zero-length region is not meaningful, so it's better not to define
it at all.  The size of this region is used in the code, but its
value will still be zero because the memory regions are defined in
statically initialized memory.

For the SC7180, the STATS_DROP memory region has a zero size and no
canaries as well.

These regions are the only place where a zero-sized region is
defined despite having no canaries.  Remove them.

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