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>

Documentation/Intel/Board/Galileo_checklist.html

@@ -79,8 +79,6 @@
 <tr bgcolor=#ffc0c0><td>Required</td><td>smm_region_size</td></tr>
 <tr bgcolor=#c0ffc0><td>Required</td><td>soc_after_ram_init</td></tr>
 <tr bgcolor=#c0ffc0><td>Required</td><td>soc_display_memory_init_params</td></tr>
-<tr bgcolor=#c0ffc0><td>Required</td><td>soc_display_mtrrs</td></tr>
-<tr bgcolor=#c0ffc0><td>Required</td><td>soc_get_variable_mtrr_count</td></tr>
 <tr bgcolor=#c0ffc0><td>Required</td><td>soc_memory_init_params</td></tr>
 <tr bgcolor=#ffffc0><td>Optional</td><td>soc_pre_ram_init</td></tr>
 <tr bgcolor=#ffffc0><td>Optional</td><td>southbridge_smi_handler</td></tr>

Documentation/Intel/SoC/soc.html

@@ -234,8 +234,6 @@ Use the following steps to locate the FSP binary:
         <a target="_blank" href="https://review.coreboot.org/gitweb?p=coreboot.git;a=blob;f=src/drivers/intel/fsp1_1/cache_as_ram.inc">src/drivers/intel/fsp1_1/cache_as_ram.inc</a>
       </li>
       <li>Add "select SOC_INTEL_COMMON" to enable the use of the files from src/soc/intel/common
-        specifically building
-        <a target="_blank" href="https://review.coreboot.org/gitweb?p=coreboot.git;a=blob;f=src/soc/intel/common/util.c">util.c</a>
       </li>
     </ol>
   </li>