arch/x86: Implement common CF9 reset

It's very common across many x86 silicon vendors, so place it in
`arch/x86/`.

Change-Id: I06c27afa31e5eecfdb7093c02f703bdaabf0594c
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/29054
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/arch/x86/Kconfig

@@ -315,3 +315,10 @@ config IDT_IN_EVERY_STAGE
 	bool
 	default n
 	depends on ARCH_X86
+
+config HAVE_CF9_RESET
+	bool
+
+config HAVE_CF9_RESET_PREPARE
+	bool
+	depends on HAVE_CF9_RESET