panfrost: Correct polygon size computations

panfrost: Correct polygon size computations

While the algorithm for computing the header size has been correct for a
while, we used a major hack to conservatively guess the body size. Let's
scrap that and figure out the algorithm we actually need to use to be
bit-identical with what the hardware expects.

We do have to be careful to add the header size to total comptued BO
size.

It's not clear how big the polygon list needs to be in practice -- but
it has to be somewhat bigger than the polygon list itself. This needs
more investigation. If we size the polygon list exactly based on the
polygon_list_size field, we get faults like:

[ 1224.219886] panfrost ff9a0000.gpu: Unhandled Page fault in AS0 at VA 0x000000001BDE8000
               Reason: TODO
               raw fault status: 0x660003C3
               decoded fault status: SLAVE FAULT
               exception type 0xC3: TRANSLATION_FAULT_LEVEL3
               access type 0x3: WRITE
               source id 0x6600

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>