OMAP: DSS2: Pass platform_device as an argument in dsi functions

The DSI interface is represented as a platform device, using the DSI platform
driver(dsi.c). The current DSI driver design is capable of running only one
instance of a DSI device. On OMAP4, there are 2 very similar DSI modules which
can be represented as instances of "omapdss_dsi" platform device.

Add member "module" in "dssdev.phy.dsi" that tells us which DSI module's lanes
the panel is connected to. Modify dsi.c functions to take the device's
platform_device struct pointer, provide functions dsi_get_dsidev_from_dssdev()
and dsi_get_dsidev_from_id() take the panel's omap_dss_device and module number
respectively, and return the platform_device pointer. Currently, the dsi struct
is declared globally and is accessed when dsi data is needed. The new pdev
argument will be used later to provide the platform device's dsi related data.

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