ARC: [DeviceTree] Convert some Kconfig items to runtime values

* mem size now runtime configured (prev CONFIG_ARC_PLAT_SDRAM_SIZE)
* core cpu clk runtime configured (prev CONFIG_ARC_PLAT_CLK)

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@secretlab.ca>

arch/arc/boot/dts/skeleton.dtsi

@@ -13,9 +13,13 @@
 
 / {
 	compatible = "snps,arc";
+	clock-frequency = <80000000>;	/* 80 MHZ */
 	#address-cells = <1>;
 	#size-cells = <1>;
 	chosen { };
 	aliases { };
-	memory { device_type = "memory"; reg = <0 0>; };
+	memory {
+		device_type = "memory";
+		reg = <0x00000000 0x10000000>;	/* 256M */
+	};
 };