x86: dts: Define a default TSC timer frequency

If for some reason, TSC timer frequency cannot be determined from
hardware, nor is it specified in the device tree, U-Boot will panic
resulting in endless reset during boot.

Let's define a default TSC timer frequency using the Kconfig value
CONFIG_X86_TSC_TIMER_FREQ (note: #include must be used instead of
/include/ otherwise the macro is not pre-processed).

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/dts/efi-x86_app.dts b/arch/x86/dts/efi-x86_app.dts
index 20150f6..04e044a 100644
--- a/arch/x86/dts/efi-x86_app.dts
+++ b/arch/x86/dts/efi-x86_app.dts
@@ -6,7 +6,8 @@
 /dts-v1/;
 
 /include/ "skeleton.dtsi"
-/include/ "tsc_timer.dtsi"
+
+#include "tsc_timer.dtsi"
 
 / {
 	model = "EFI x86 Application";
@@ -16,10 +17,6 @@
 		stdout-path = &serial;
 	};
 
-	tsc-timer {
-		clock-frequency = <1000000000>;
-	};
-
 	serial: serial {
 		compatible = "efi,uart";
 	};