Remove configuration of Ac-bias pins

Ac-bias pins need to be configured only for passive matrix displays. Remove
acbi and acb fields in omap_dss_device and their configuration in panel
drivers. Don't program these fields in DISP_POL_FREQo register any more.

The panel driver for sharp-ls037v7dw01, and the panel config for
Innolux AT070TN8 in generic dpi panel driver set acb to a non zero value. This
is most likely carried over from the old omapfb driver which supported passive
matrix displays.

Cc: Thomas Weber <weber@corscience.de>
Signed-off-by: Archit Taneja <archit@ti.com>