rtc: ds1302: rewrite using SPI

DS1302 is an half-duplex SPI device. The driver respects this fact now.
Pin configurations should be implemented using SPI subsystem.
Signed-off-by: Sergei Ianovich <ynvich@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

Documentation/devicetree/bindings/rtc/maxim-ds1302.txt

+* Maxim/Dallas Semiconductor DS-1302 RTC
+
+Simple device which could be used to store date/time between reboots.
+
+The device uses the standard MicroWire half-duplex transfer timing.
+Master output is set on low clock and sensed by the RTC on the rising
+edge. Master input is set by the RTC on the trailing edge and is sensed
+by the master on low clock.
+
+Required properties:
+
+- compatible : Should be "maxim,ds1302"
+
+Required SPI properties:
+
+- reg : Should be address of the device chip select within
+  the controller.
+
+- spi-max-frequency : DS-1302 has 500 kHz if powered at 2.2V,
+  and 2MHz if powered at 5V.
+
+- spi-3wire : The device has a shared signal IN/OUT line.
+
+- spi-lsb-first : DS-1302 requires least significant bit first
+  transfers.
+
+- spi-cs-high: DS-1302 has active high chip select line. This is
+  required unless inverted in hardware.
+
+Example:
+
+spi@901c {
+	#address-cells = <1>;
+	#size-cells = <0>;
+	compatible = "icpdas,lp8841-spi-rtc";
+	reg = <0x901c 0x1>;
+
+	rtc@0 {
+		compatible = "maxim,ds1302";
+		reg = <0>;
+		spi-max-frequency = <500000>;
+		spi-3wire;
+		spi-lsb-first;
+		spi-cs-high;
+	};
+};

drivers/rtc/Kconfig

@@ -634,6 +634,15 @@ config RTC_DRV_M41T94
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-m41t94.
 
+config RTC_DRV_DS1302
+	tristate "Dallas/Maxim DS1302"
+	depends on SPI
+	help
+	  If you say yes here you get support for the Dallas DS1302 RTC chips.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-ds1302.
+
 config RTC_DRV_DS1305
 	tristate "Dallas/Maxim DS1305/DS1306"
 	help
@@ -834,12 +843,6 @@ config RTC_DRV_DS1286
 	help
 	  If you say yes here you get support for the Dallas DS1286 RTC chips.
 
-config RTC_DRV_DS1302
-	tristate "Dallas DS1302"
-	depends on SH_SECUREEDGE5410
-	help
-	  If you say yes here you get support for the Dallas DS1302 RTC chips.
-
 config RTC_DRV_DS1511
 	tristate "Dallas DS1511"
 	depends on HAS_IOMEM