[ARM] tegra: stingray: Add fixed regulator for panel enable

[ARM] tegra: stingray: Add fixed regulator for panel enable

Due to a problem with the hardware design, a voltage divider
is created on the i2c bus when the panel is turned off.  This
can cause problems with other devices on that bus.  To work
around, a fixed regulator has been created representing the panel
power.  This regulator must be enabled when devices on that i2c
bus are in use, even if the panel is otherwise off.

Change-Id: I78d9a3b29e69c1cffd5e8df23025b186527f31b3
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>