OMAP: RX51: Add "vdds_sdi" supply voltage for SDI

The SDI Display subsystem needs access to the vdds_sdi supply
regulator. This is TWL4030's VAUX1 supply on RX-51.

Signed-off-by: Roger Quadros <roger.quadros@nokia.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>