configs/config.asrock_b85m_pro4...: Clarify its purpose

The purpose of this config is to build-test the individual options, not
their combination. So, for instance, if it would be hard to keep options
x, y and z build together in the future, this config shouldn't block a
change but should instead be adapted, e.g. split into multiple chunks.

Change-Id: Ibd8f6513fae6cd02fcf889d2510dc7e0a97ce40c
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47068
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

configs/config.asrock_b85m_pro4.debug_smmstore_hotplug_gcov_ubsan_em100

@@ -1,4 +1,7 @@
-# Not meant for actual use. Exercises, among other things:
+# Not meant for actual use, but rather to build-test individual options.
+# If keeping this combination of options buildable becomes too hard in
+# the future, then this config can be split into several smaller chunks.
+# Exercises, among other things:
 # + Code coverage
 # + UBSAN
 # + Debug options