vp9: fix memory alloc for adaptive_rd_thresh_row_mt.

vp9: fix memory alloc for adaptive_rd_thresh_row_mt.

When the feature is enabled and the memory is not available, allocate
it. There was a case where speed feature changed in the middle of stream
but the number of tiles stayed the same, memory was not re-allocated.

Another case is where speed for base layer is different than that of
higher quality layers (same resolution). Removed the speed constraints
forcing base layer using same speed setting.

Thus the memory for adaptive_rd_thresh_row_mt stayed NULL but the
feature was enabled.

Add an end to end test to cover this case.

Change-Id: I2f1f802ef98a554571b30094d3600b9439228457