ARM: omap3_beagle: Enable DM_PMIC and DM_REGULATOR

Enabling DM_PMIC, DM_REGULATOR_FIXED, and DM_REGULATOR_GPIO
gives us the ability to better monitor voltages and enable
hardware through the device tree. The TL4030 (TPS65950) is
not yet migrated to DM, so this patch only enables the fixed
and GPIO controlled regulators.

Based on commit [1][2].

[1] a40d3cc8
[2] 2448e42d

Signed-off-by: Romain Naour <romain.naour@gmail.com>