ARM: dts: socfpga: Add a 3.3V fixed regulator node

Without the 3.3V regulator node, the SDMMC driver will give these warnings:

dw_mmc ff704000.dwmmc0: No vmmc regulator found
dw_mmc ff704000.dwmmc0: No vqmmc regulator found

This patch adds the regulator node, and points the SD/MMC to the regulator.

Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
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v3: Rename nodes to have schematic-name_regulator and remove "boot-on" and
    "always-on"
v2: Move the regulator nodes to their respective board dts file and
    correctly rename them to match the schematic