imx6: Add ds1307 RTC to kernel for working hctosys

Otherwise if we use ds1307 as kernel module, hctosys fails as ds1307 is
being initialized later then hctosys:

 [    2.427349] hctosys: unable to open rtc device (rtc0)
 [    3.714263] snvs_rtc 20cc000.snvs:snvs-rtc-lp: rtc core: registered 20cc000.snvs:snvs-r as rtc1
 [    8.990061] rtc-ds1307 3-006f: rtc core: registered mcp7941x as rtc0

Signed-off-by: Petr Štetiar <ynezz@true.cz>

target/linux/imx6/config-4.4

@@ -163,6 +163,7 @@ CONFIG_GENERIC_STRNLEN_USER=y
 # CONFIG_GIANFAR is not set
 CONFIG_GLOB=y
 CONFIG_GPIOLIB=y
+CONFIG_GPIOLIB_IRQCHIP=y
 CONFIG_GPIO_DEVRES=y
 CONFIG_GPIO_GENERIC=y
 CONFIG_GPIO_MXC=y
@@ -349,6 +350,7 @@ CONFIG_REGULATOR_PFUZE100=y
 CONFIG_RFS_ACCEL=y
 CONFIG_RPS=y
 CONFIG_RTC_CLASS=y
+CONFIG_RTC_DRV_DS1307=y
 # CONFIG_RTC_DRV_IMXDI is not set
 # CONFIG_RTC_DRV_MXC is not set
 CONFIG_RWSEM_SPIN_ON_OWNER=y