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>

src/cpu/intel/fsp_model_406dx/Kconfig

@@ -29,6 +29,7 @@ config CPU_SPECIFIC_OPTIONS
 	select SSE2
 	select UDELAY_LAPIC
 	select SUPPORT_CPU_UCODE_IN_CBFS
+	select MICROCODE_BLOB_NOT_IN_BLOB_REPO
 	select PARALLEL_CPU_INIT
 	select TSC_SYNC_MFENCE
 	select LAPIC_MONOTONIC_TIMER

src/cpu/intel/microcode/Makefile.inc

@@ -4,5 +4,3 @@
 ################################################################################
 ramstage-$(CONFIG_SUPPORT_CPU_UCODE_IN_CBFS) += microcode.c
 romstage-$(CONFIG_SUPPORT_CPU_UCODE_IN_CBFS) += microcode.c
-
-cpu_microcode_bins += $(call strip_quotes,$(CONFIG_CPU_UCODE_BINARIES))