image: p_median3x3: Add function implementation
image: p_median3x3: Add function implementation

Targeting memory traffic efficiency.

Signed-off-by: Mateusz Kacprzak <bc894a8e1b1a34aed79275f42996b76d0cbc3c43@yandex.ru>

eliteraspberries/pal,mateunho/pal,olajep/pal,parallella/pal,aolofsson/pal,debug-de-su-ka/pal,Adamszk/pal3,debug-de-su-ka/pal,debug-de-su-ka/pal,eliteraspberries/pal,8l/pal,parallella/pal,eliteraspberries/pal,twocs/pal,twocs/pal,olajep/pal,parallella/pal,debug-de-su-ka/pal,Adamszk/pal3,8l/pal,8l/pal,debug-de-su-ka/pal,mateunho/pal,aolofsson/pal,parallella/pal,eliteraspberries/pal,8l/pal,olajep/pal,twocs/pal,RafaelRMA/pal,twocs/pal,eliteraspberries/pal,RafaelRMA/pal,Adamszk/pal3,mateunho/pal,mateunho/pal,aolofsson/pal,olajep/pal,RafaelRMA/pal,RafaelRMA/pal,parallella/pal,aolofsson/pal,mateunho/pal,Adamszk/pal3