tree: Make internal functions static

None of these functions are used outside of the files they are defined
in, so make them all static.

Change-Id: Ie9cbe12d289bcedacf2f1bf483ae64ef8039ccc1
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/33667
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/edi.c b/edi.c
index 2afd032..bd5b269 100644
--- a/edi.c
+++ b/edi.c
@@ -457,7 +457,7 @@
 	return 0;
 }
 
-int edi_shutdown(void *data)
+static int edi_shutdown(void *data)
 {
 	struct flashctx *flash;
 	int rc;