Add config flags and macros to control ext-inter

Adds a dependent config flag 'interintra' to turn on/off interintra
modes altogether.
Adds a dependent config flag 'wedge' to turn on/off wedge compound
for both interinter and interintra.

Adds another macro to change wedge predictors to use
only 0, 1/2, or 1 weights.

From now, use
--enable-ext-inter --enable-wedge --enable-interintra to get the
same behavior as the old --enable-ext-inter.

Change-Id: I2e787e6994163b6b859a9d6431b87c4217834ddc
5 files changed