The dsi related data structure currently creates one global instance of itself
which is accessed by dsi functions. Remove this global structure instance and
declare the struct as dsi_data. Modify dsi_init() to allocate a "dsi_data"
structure for each platform device instance. Link this data with the device's
platform_device pointer. Create the function dsi_get_dsidrv_data() which takes
the pdev and return a pointer to the device's dsi_data.

Make dsi_get_dsidev_id() return only 0 for now, this will be removed once the
name of the DSI platform device is changed to the device instance form, like
"omapdss_dsi.0" and "omapdss_dsi.1" etc.
Signed-off-by: NArchit Taneja <archit@ti.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>