With this patch affine or homography models can be enabled
by simply changing the value of the GLOBAL_TRANS_TYPES
macro in common/mv.h to 4 and 5 respectively. Currently
it is left at supporting only rotzoom. There is a small
gain with enabling affine.

Also refactors costing to change based on the model type.

Change-Id: I46c1759de06c42c176c64ec21307ff347ddcc259