soc/intel/common: Bring DISPLAY_MTRRS into the light

Initially, I wanted to move only the Kconfig DISPLAY_MTRRS into the
"Debug" menu. It turned out, though, that the code looks rather generic.
No need to hide it in soc/intel/.

To not bloat src/Kconfig up any further, start a new `Kconfig.debug`
hierarchy just for debug options.

If somebody wants to review the code if it's 100% generic, we could
even get rid of HAVE_DISPLAY_MTRRS.

Change-Id: Ibd0a64121bd6e4ab5d7fd835f3ac25d3f5011f24
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/29684
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/x86/postcar.c

@@ -16,9 +16,9 @@
 #include <arch/cpu.h>
 #include <cbmem.h>
 #include <console/console.h>
+#include <cpu/x86/mtrr.h>
 #include <main_decl.h>
 #include <program_loading.h>
-#include <soc/intel/common/util.h>
 
 /*
  * Systems without a native coreboot cache-as-ram teardown may implement
@@ -35,9 +35,7 @@ void main(void)
 	/* Recover cbmem so infrastruture using it is functional. */
 	cbmem_initialize();
 
-	/* Display the MTRRs */
-	if (IS_ENABLED(CONFIG_DISPLAY_MTRRS))
-		soc_display_mtrrs();
+	display_mtrrs();
 
 	/* Load and run ramstage. */
 	run_ramstage();