x86: bootblock: remove linking and program flow from build system

The build system was previously determining the flow
and linking scripts bootblock code by the order of files
added to the bootblock_inc bootblock-y variables.Those
files were then concatenated together and built by a myriad of
make rules.

Now bootblock.S and bootblock.ld is added so that bootblock
can be built and linked using the default build rules.
CHIPSET_BOOTBLOCK_INCLUDE is introduced in order to allow the
chipset code to place include files in the path of the bootblock
program -- a replacement for the chipset_bootblock_inc
make variable.

BUG=chrome-os-partner:44827
BRANCH=None
TEST=Built vortex, rambi, and some asus boards.

Change-Id: Ida4571cbe6eed65e77ade98b8d9ad056353c53f9
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/11495
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/soc/intel/skylake/Kconfig

@@ -200,4 +200,8 @@ config UART_DEBUG
 	select DRIVERS_UART_8250MEM
 	select DRIVERS_UART_8250MEM_32
 
+config CHIPSET_BOOTBLOCK_INCLUDE
+	string
+	default "soc/intel/skylake/bootblock/timestamp.inc"
+
 endif

src/soc/intel/skylake/Makefile.inc

@@ -1,6 +1,5 @@
 ifeq ($(CONFIG_SOC_INTEL_SKYLAKE),y)
 
-subdirs-y += bootblock
 subdirs-y += microcode
 subdirs-y += romstage
 subdirs-y += ../../../cpu/intel/microcode

src/soc/intel/skylake/bootblock/Makefile.inc

@@ -1 +0,0 @@
-chipset_bootblock_inc += $(src)/soc/intel/skylake/bootblock/timestamp.inc