Update CTS support for AVG_POOL2D and MAX_POOL2D.

Enable stable random, random const and generator test selector.

Also fix up so that FP special tests are always chosen by the
test selector.

Signed-off-by: Eirini Vlassi Pandi <eirini.vlassipandi@arm.com>
Signed-off-by: Jeremy Johnson <jeremy.johnson@arm.com>
Change-Id: I5d44f0f2291f3e5863613e69f328fedfbc0b4ac8