OMAP: DSS2: Use request / release calls in Taal for DSI Virtual Channels.

OMAP: DSS2: Use request / release calls in Taal for DSI Virtual Channels.

Taal driver used to take a hard coded Macro for Virtual Channel and the VC_ID.
The Taal panel driver now requests for a Virtual channel through the
omap_dsi_request_vc() call in taal_probe().

The channel number returned by the request_vc() call is used for sending command
and data to the Panel. The DSI driver automatically configures the Virtual
Channel's source to either Video Port or L4 Slave port based on what the panel
driver is using it for.

The driver uses omap_dsi_release_vc() to free the VC specified by the panel.
taal_remove() or when a request_vc() call fails.

Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>