And also add Kconfig option for selecting ELDO3 voltage. The reason
for having this option is that the Android kernel sets ELDO3 to
1.2V when powering up LCD in the case if 'lcd_if' configuration
variable is set to 6 (LCD_IF_EXT_DSI) in the FEX file. Most likely
to supply power for a SSD2828 chip.

However on the MSI Primo81 tablet, which is using this particular
'lcd_if = 6' setup for LCD, setting the ELDO3 voltage appears to
be unnecessary and it works regardless. Having no schematics of
this tablet, I can only guess that 1.2V is supplied to SSD2828
in some other way.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>