x86: Move itss.c from Apollo Lake to a more generic location

The Interrupt Timer Subsystem (ITSS) is not specific to Apollo Lake, so
move it to a common location within arch/x86.

Signed-off-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
[bmeng: conditionally build itss.c]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/apollolake/Makefile

@@ -19,7 +19,6 @@ obj-y += fsp_s.o
 endif
 
 obj-y += hostbridge.o
-obj-y += itss.o
 obj-y += lpc.o
 obj-y += p2sb.o
 obj-y += pch.o

arch/x86/cpu/intel_common/Makefile

@@ -27,6 +27,9 @@ obj-y += microcode.o
 endif
 endif
 obj-y += pch.o
+ifdef CONFIG_INTEL_APOLLOLAKE
+obj-y += itss.o
+endif
 
 ifdef CONFIG_SPL
 ifndef CONFIG_SPL_BUILD