ASoC: OMAP ABE: Update ping/pong mode to support 4 buffers.

ASoC: OMAP ABE: Update ping/pong mode to support 4 buffers.

Current ping/pong mode is supporting only 2 buffers. We can extend
the number of buffer to 4 in order to fit with current Audio HAL.
This will enable the selection of Ping/pong instead of CBPr and lead
to longer time between the different OMAP L3 wake up.

Remove duplication of structure definition until rework of ABE code.

Change-Id: I2037f50bf46b530f6d22c8306db9f44d9c2856e4
Signed-off-by: Sebastien Guiriec <s-guiriec@ti.com>