Revert "remove CONFIG_SERIAL_CPU_INIT"

This reverts commit 78efc4c36c.

The broadcast patch was reverted, so this commit should also
be reverted. The reason for reverting the broadcast patch:

It turned out that sending IPIs via broadcast doesn't work on
Sandybridge. We tried to come up with a solution, but didn't
found any so far. So revert the code for now until we have
a working solution.

Change-Id: I05c27dec55fa681f455215be56dcbc5f22808193
Signed-off-by: Sven Schnelle <svens@stackframe.org>
Reviewed-on: http://review.coreboot.org/1380
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/cpu/intel/model_206ax/Kconfig

@@ -18,6 +18,10 @@ config BOOTBLOCK_CPU_INIT
 	string
 	default "cpu/intel/model_206ax/bootblock.c"
 
+config SERIAL_CPU_INIT
+	bool
+	default n
+
 config SMM_TSEG_SIZE
 	hex
 	default 0x800000

src/cpu/x86/Kconfig

@@ -1,3 +1,7 @@
+config SERIAL_CPU_INIT
+	bool
+	default y
+
 config WAIT_BEFORE_CPUS_INIT
 	bool
 	default n