regulator: Add support for QCOM PMIC VBUS booster

Some Qualcomm PMICs have the capability to source the VBUS output to
connected peripherals.  This driver will register a regulator to the
regulator list to enable or disable this source by an external driver.

Signed-off-by: Wesley Cheng <wcheng@codeaurora.org>
Link: https://lore.kernel.org/r/20200626185516.18018-5-wcheng@codeaurora.org
Signed-off-by: Mark Brown <broonie@kernel.org>