ARM: dts: am4372: fix clock source for arm twd and global timers

ARM TWD and Global timer are clocked by PERIPHCLK which is MPU_CLK/2.
But now they are clocked by dpll_mpu_m2_ck == MPU_CLK and, as result.
Timekeeping core misbehaves. For example, execution of command
"sleep 5" will take 10 sec instead of 5.

Hence, fix it by adding mpu_periphclk ("fixed-factor-clock") and use
it for clocking ARM TWD and Global timer (same way as on OMAP4).

Cc: Tony Lindgren <tony@atomide.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Tero Kristo <t-kristo@ti.com>
Fixes:commit 8cbd4c2f ("arm: boot: dts: am4372: add ARM timers and SCU nodes")
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am4372.dtsi

@@ -74,7 +74,7 @@ global_timer: timer@48240200 {
 		reg = <0x48240200 0x100>;
 		interrupts = <GIC_PPI 11 IRQ_TYPE_LEVEL_HIGH>;
 		interrupt-parent = <&gic>;
-		clocks = <&dpll_mpu_m2_ck>;
+		clocks = <&mpu_periphclk>;
 	};
 
 	local_timer: timer@48240600 {
@@ -82,7 +82,7 @@ local_timer: timer@48240600 {
 		reg = <0x48240600 0x100>;
 		interrupts = <GIC_PPI 13 IRQ_TYPE_LEVEL_HIGH>;
 		interrupt-parent = <&gic>;
-		clocks = <&dpll_mpu_m2_ck>;
+		clocks = <&mpu_periphclk>;
 	};
 
 	l2-cache-controller@48242000 {

arch/arm/boot/dts/am43xx-clocks.dtsi

@@ -259,6 +259,14 @@ dpll_mpu_m2_ck: dpll_mpu_m2_ck {
 		ti,invert-autoidle-bit;
 	};
 
+	mpu_periphclk: mpu_periphclk {
+		#clock-cells = <0>;
+		compatible = "fixed-factor-clock";
+		clocks = <&dpll_mpu_m2_ck>;
+		clock-mult = <1>;
+		clock-div = <2>;
+	};
+
 	dpll_ddr_ck: dpll_ddr_ck {
 		#clock-cells = <0>;
 		compatible = "ti,am3-dpll-clock";