MLBEDSW-6563: networks failing with memory area exceeded in vela

 - For allocations that have a hard memory limit the Hill Climb allocator
should be given more attempts to find a solution that would fit
 - The fix is to use a memory limit when there is a hard constraint, and
a minimum iteration count, reset on every improvement, when there is a soft
constraint
 - Added maximum number iterations CLI option

Signed-off-by: Tim Hall <tim.hall@arm.com>
Change-Id: I19ff53a0b68412de280263626778a3102cbe52fa