power: twl6030: Enable VAUX1 for eMMC power, depending on BOOT2 value

This enables the VAUX1 supply, used for eMMC power in standard configurations.
Its voltage is determined by the value of the BOOT2 pin of the TWL6030.

Note that the TWL6030 might already have enabled this regulator at startup
(depending on the value of the BOOT3 pin of the TWL6030), according to the
TWL6030 datasheet.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>