Use reconstructed pixels for intra prediction

This commit makes the speed -6 and above use the reconstructed
boundary pixels for precise intra prediction. This allows more
intra prediction modes to be tested in the non-RD coding process.

Enabling horizontal and vertical intra prediction modes can
improve the speed -6 compression performance for rtc set
by 0.331%.

Change-Id: I3a99f9d12c6af54de2bdbf28c76eab8e0905f744