This is added as part of ALT_INTRA experiment.

This uses interpolation between top row and estimated bottom row; as
well as left column and estimated right column to generate the
predicted block.The interpolation is done using a predefined weight
array.

Based on experiments, the currently chosen weight array was created
to represent a quadratic curve, but can be tuned further if needed.

Improvement from baseline on Derf set:
ALL Keyframes: 1.279%

Improvement from existing ALT_INTRA:
ALL Keyframes: 1.146%

Change-Id: I12637fa1b91bd836f1c59b27d6caee2004acbdd4