power: qcom_smbb: Make an extcon for usb cable detection

On these PMICs the usb cable connection/disconnection is
indicated by the usb-valid interrupt being high or low
respectively. Let's make an extcon for that, so we can notify usb
drivers of the cable state.

Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
diff --git a/drivers/power/Kconfig b/drivers/power/Kconfig
index 421770d..6bff735 100644
--- a/drivers/power/Kconfig
+++ b/drivers/power/Kconfig
@@ -393,6 +393,7 @@
 	tristate "Qualcomm Switch-Mode Battery Charger and Boost"
 	depends on MFD_SPMI_PMIC || COMPILE_TEST
 	depends on OF
+	depends on EXTCON
 	help
 	  Say Y to include support for the Switch-Mode Battery Charger and
 	  Boost (SMBB) hardware found in Qualcomm PM8941 PMICs.  The charger