Makefile.inc: Generate master header and pointer as C structs

The makefiles don't like cbfs file names with spaces in them so update
the file name with '_' instead of spaces. To keep the master header at
the top of cbfs, add a placeholder.

This removes the need to handle the cbfs master header in cbfstool.
This functionality will be dropped in a later CL.

On x86 reserve some space in the linker script to add the pointer.
On non-x86 generate a pointer inside a C struct file.

As a bonus this would actually fix the master header pointer mechanism
on Intel/APL as only the bootblock inside IFWI gets memory mapped.

TESTED on thinkpad X201: SeaBIOS correctly finds the cbfs master
header.

Change-Id: I3ba01be7da1f09a8cac287751497c18cda97d293
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59132
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

Makefile.inc

@@ -1120,18 +1120,7 @@ else # ifeq ($(CONFIG_ARCH_X86),y)
 	$(CBFSTOOL) $@.tmp write -u \
 		-r BOOTBLOCK \
 		-f $(objcbfs)/bootblock.bin
-	# make space for the CBFS master header pointer. "ptr_" is just
-	# arbitrary 4 bytes that will be overwritten by add-master-header.
-	printf "ptr_" > $@.tmp.2
-	$(CBFSTOOL) $@.tmp add \
-		-f $@.tmp.2 \
-		-n "header pointer" \
-		-t "cbfs header" \
-		-b -4 \
-		$(CBFSTOOL_ADD_CMD_OPTIONS)
-	rm -f $@.tmp.2
 endif # ifeq ($(CONFIG_ARCH_X86),y)
-	$(CBFSTOOL) $@.tmp add-master-header $(TS_OPTIONS) $(CBFSTOOL_ADD_CMD_OPTIONS)
 	$(prebuild-files) true
 	mv $@.tmp $@
 else # ifneq ($(CONFIG_UPDATE_IMAGE),y)