power: qpnp-smbcharger: support external boost for OTG

During DC charging, some devices may want to support USB OTG with an
external boost. The PMI8994 has an 5V audio boost that can be utilized
to provide the 5V that OTG requires.

Add the usb_otg_switch fixed regulator to enable the switch that
connects the boost with USBIN via PMI8994 GPIO 5.

Add the smbcharger_external_otg regulator to disable the usb charge path
when the 5V is provided.

The layout of the regulator supply chain will be the following:
	- usb_otg_switch
		- fixed regulator that controlls gpio to enable/disable
		  OVP FET
	- supplied by: smbcharger_external_otg
		- smbcharger regulator that disables usb charging and USB
		  source detect
	- supplied by: pmi8994_boost_5v
		- rpm regulator that enables the 5V smart boost in the
		  PMI8994.

The usb_otg_switch can be used in place of smbcharger_charger_otg to
provide the 5V in place of the charger operating in reverse if specified
in the devicetree.

CRs-Fixed: 659471
Change-Id: Iad7929e2dc6eac4e85351074267dd8f5ac4292e9
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>