twl4030: VMMC2 3.2V enable on MMC init

This enables the VMMC2 LDO, which powers the MMC2 device.
When the device starts from MMC2, this has already been enabled by the BootROM,
but when starting from peripheral boot (USB, UART), it is not the case.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>