Untangle CBFS microcode updates

The option to specify a binary file name was added later for platforms
that do not provide microcode updates in our blobs repository. Alas,
it wasn't visible what platforms these are. And if you specified a file
for a platform that already had one, they were all included together.

Make it visible which platforms don't provide binaries with the new con-
figs MICROCODE_BLOB_NOT_IN_BLOB_REPO, MICROCODE_BLOB_NOT_HOOKED_UP and
MICROCODE_BLOB_UNDISCLOSED. Based on that we can decide if we want to
include binaries by default or explicitly show that no files are inclu-
ded (default to CPU_MICROCODE_CBFS_NONE).

Also split CPU_MICROCODE_CBFS_GENERATE into the more explicit
CPU_MICROCODE_CBFS_DEFAULT_BINS and CPU_MICROCODE_CBFS_EXTERNAL_BINS.
And clean up the visibility of options: Don't show CBFS related options
on platforms that don't support it and don't show external file options
if the platform uses special rules for multiple files (CPU_MICROCODE_
MULTIPLE_FILES).

Change-Id: Ib403402e240d3531640a62ce93b7a93b4ef6ca5e
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/29934
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Makefile.inc

@@ -1054,7 +1054,7 @@ ifeq ($(CONFIG_CPU_MICROCODE_CBFS_EXTERNAL_HEADER),y)
 	$(FIT_OPTIONS)
 endif
 
-ifeq ($(CONFIG_CPU_MICROCODE_CBFS_GENERATE),y)
+ifeq ($(CONFIG_USE_CPU_MICROCODE_CBFS_BINS),y)
 	@printf "    UPDATE-FIT\n"
 	$(CBFSTOOL) $@.tmp update-fit -n cpu_microcode_blob.bin -x $(CONFIG_CPU_INTEL_NUM_FIT_ENTRIES) \
 	$(FIT_OPTIONS)