i2c: Separate Kconfig option for i2c-smbus

Having a separate Kconfig option for i2c-smbus makes it possible to
build that support as a module even when i2c-core itself is built-in.
Bus drivers which implement SMBus alert should select this option, so
in most cases this option is hidden and the user doesn't have to care
about it.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Trent Piepho <tpiepho@freescale.com>
diff --git a/drivers/i2c/Makefile b/drivers/i2c/Makefile
index 7111c93..acd0250 100644
--- a/drivers/i2c/Makefile
+++ b/drivers/i2c/Makefile
@@ -3,7 +3,8 @@
 #
 
 obj-$(CONFIG_I2C_BOARDINFO)	+= i2c-boardinfo.o
-obj-$(CONFIG_I2C)		+= i2c-core.o i2c-smbus.o
+obj-$(CONFIG_I2C)		+= i2c-core.o
+obj-$(CONFIG_I2C_SMBUS)		+= i2c-smbus.o
 obj-$(CONFIG_I2C_CHARDEV)	+= i2c-dev.o
 obj-y				+= busses/ chips/ algos/