Fixes BHV-15753

## Issue
There's a circular dependency between `calcBoundaries` and `_getScrollBounds` where the former calculates the `ScrollMath.bottomBoundary` using the `maxTop` retrieved from the latter but the latter needs the `bottomBoundary` to correctly enable the paging controls but it hasn't been calculated yet.

## Fix
Refactor the paging control logic into its own method and have it called in calcBoundaries since it's establishing the data necessary to do the work.

Enyo-DCO-1.1-Signed-off-by: Ryan Duffy (ryan.duffy@lge.com)