usb: host: xhci-mtk: Simplify supplies handling with regulator_bulk

usb: host: xhci-mtk: Simplify supplies handling with regulator_bulk

Remove the custom functions xhci_mtk_ldos_{enable,disable}() by
switching to using regulator_bulk to perform the very same thing,
as the regulators are always either both enabled or both disabled.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220214111905.77903-1-angelogioacchino.delregno@collabora.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>