power: supply: pm8916_lbc: observe EXTCON config setting

When CONFIG_EXTCON=m and CONFIG_CHARGER_PM8916_LBC=y, there are
build errors. Fix them by having CHARGER_PM8916_LBC depend on the
setting of EXTCON.

aarch64-linux-ld: drivers/power/supply/pm8916_lbc.o: in function `pm8916_lbc_charger_state_changed_irq':
pm8916_lbc.c:(.text+0xe8): undefined reference to `extcon_set_state_sync'
aarch64-linux-ld: drivers/power/supply/pm8916_lbc.o: in function `pm8916_lbc_charger_probe':
pm8916_lbc.c:(.text+0x638): undefined reference to `devm_extcon_dev_allocate'
aarch64-linux-ld: pm8916_lbc.c:(.text+0x650): undefined reference to `devm_extcon_dev_register'
aarch64-linux-ld: pm8916_lbc.c:(.text+0x688): undefined reference to `extcon_set_state_sync'

Fixes: f8d7a3d21160 ("power: supply: Add driver for pm8916 lbc")
Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Nikita Travkin <[e-mail]>
Cc: Sebastian Reichel <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Sebastian Reichel <[e-mail]>

drivers/power/supply/Kconfig

···
 config CHARGER_PM8916_LBC
 	tristate "Qualcomm PM8916 Linear Battery Charger support"
 	depends on MFD_SPMI_PMIC || COMPILE_TEST
+	depends on EXTCON || !EXTCON
 	help
 	  Say Y here to add support for Linear Battery Charger block
 	  found in some Qualcomm PMICs such as PM8916. This hardware