msm: vidc: Add new MBI mode

Add new MBI mode for configuring encoder to produce both
forward and backward motion vectors. MBI information is
embedded in the extradata associated with corresponding
bitstream buffer. When this mode is enabled video encoders
steady state behavior is as follows:

+------+-------+-------------------------------------+
| Time | Input |               Output                |
+------+-------+-------------------------------------+
|  T1  |   A   |                                     |
+------+-------+-------------------------------------+
|  T2  |   B   | encoded(A) + MBI(A<-B) + MBI (A->B) |
+------+-------+-------------------------------------+
|  T3  |   C   | encoded(B) + MBI(B<-C) + MBI (B->C) |
+------+-------+-------------------------------------+

Change-Id: Iafb1cf6670930a4b1a2abff009c1034a89b25b5b
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>