BGA decoupling capacitors placement
All the ground balls go down to the ground plane by means of local vias, and all the power pins on any given rail go down to a power plane region on the appropriate rail, then you place the caps as per the note and connect them to the appropriate places.

Probably the small caps go on the back under the appropriate power plane region and just via thru to the plane and ground (Two vias per cap terminal are better then one when you can fit them).