ARM: at91/dt: drop deprecated mainck node from pmc

The clock-frequency property became obsolete since the rework of the main
clock driver in 3.16 (see commit 27cb1c20).

It now get and uses the clock-frequency from the main_xtal node.
Signed-off-by: Gaël PORTAY <g.portay@overkiz.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/at91-sama5d3_xplained.dts

@@ -215,12 +215,6 @@ pinctrl_usba_vbus: usba_vbus {
 					};
 				};
 			};
-
-			pmc: pmc@fffffc00 {
-				main: mainck {
-					clock-frequency = <12000000>;
-				};
-			};
 		};
 
 		nand0: nand@60000000 {

arch/arm/boot/dts/at91sam9rlek.dts

@@ -181,12 +181,6 @@ pinctrl_board_mmc0: mmc0-board {
 				};
 			};
 
-			pmc: pmc@fffffc00 {
-				main: mainck {
-					clock-frequency = <12000000>;
-				};
-			};
-
 			watchdog@fffffd40 {
 				status = "okay";
 			};

arch/arm/boot/dts/sama5d3xcm.dtsi

@@ -67,12 +67,6 @@ ethernet-phy@7 {
 					rxd3-skew-ps = <400>;
 				};
 			};
-
-			pmc: pmc@fffffc00 {
-				main: mainck {
-					clock-frequency = <12000000>;
-				};
-			};
 		};
 
 		nand0: nand@60000000 {