util/sconfig: Re-factor emitting of headers to static.c

This change removes call to add_header from parsing functions and
moves it to a local function within main.c. It also adds a new
function emit_headers that is responsible for creating the linked list
for chip headers and emitting those to static.c

BUG=b:80081934
TEST=Verified that static.c for all files compiled using abuild is the
same with and without this change.

Change-Id: I24d526e81323115d3cc927242a4b9e49414afbe0
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/26726
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

util/sconfig/sconfig.h

@@ -110,7 +110,6 @@ void fold_in(struct device *parent);
 
 void postprocess_devtree(void);
 struct chip *new_chip(char *path);
-void add_header(struct chip *chip);
 struct device *new_device(struct device *parent, struct device *busdev,
 			  struct chip *chip, const int bus, const char *devnum,
 			  int enabled);