power: supply: qcom_smbb: add regulator dependency

The added regulator dependency in the smbb driver causes build errors
when regulators are disabled, e.g. in randconfig build testing:

drivers/power/supply/qcom_smbb.o: In function `smbb_chg_otg_is_enabled':
qcom_smbb.c:(.text.smbb_chg_otg_is_enabled+0x18): undefined reference to `rdev_get_drvdata'
drivers/power/supply/qcom_smbb.o: In function `smbb_charger_probe':
qcom_smbb.c:(.text.smbb_charger_probe+0x410): undefined reference to `devm_regulator_register'

This adds a Kconfig dependency to avoid the link error.

Fixes: 61274eff ("power: supply: qcom_smbb: Add otg regulator for control of vbus")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sebastian Reichel <sre@kernel.org>