In HwBuffer, split Setup into Setup, GetMinUndequeued and SetBufferCount since
we want to control the buffer count logic from omxil.c.

Some OMX components (like OMX.TI.*.Decoder) may have nBufferCountActual that is
greater than nBufferCountMin + min_undequeued. In that case we decreased the
number of buffer wanted by the component and had an undefined behavior.

In order to fix it, we need to increase nBufferCountActual value from the
component only when it's smaller than nBufferCountMin + min_undequeued.
Signed-off-by: Martin Storsjö <martin@martin.st>