To compute a large convolution, we tile the operation into two levels of
"folds". First, the kernels are tiled into (numKerns / peArrayCols) weight
folds (as each PE column will finish a kernel), and within each weight fold,
each output feature map is further tiled into (outputRows * outputCols /
peArrayRows) output folds (as each PE row is responsible for producing a output
channel). Each PE row has a commit unit that collects finished results from the
row and writes the data to the output scratchpad. The current write size is
always set to the line size of the scratchpad, which is not correct for a small
PE column size where the entire row doesn't form a line. This commit fixes this
by taking into account when peArrayCols is smaller than elemsInLine.

Also, this also fixes the incorrect initial tensor iterator place for the
commit units.

Change-Id: Iacc69f5d4cfa12512f25a19879b7e1aaa292a9d9

Change-Id: I18ff5af077753a776f382ad386529cace5b9ed8e