ARM: OMAP: add vdds_dsi supply for omapdss_dpi.0

DPI driver gets currently the vdds_dsi regulator via omapdss device.
This is not correct, and we'll change the DPI driver to get the
regulator directly via omapdss_dpi.0 device.

This patch changes the relevant board files to add vdds_dsi supply for
omapdss_dpi.0 device.

Note that the vdds_dsi supply for omapdss device is still left there, as
the current display driver uses it. When both the board files and the
display driver has been changed, we can remove the unused supply.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>