util/kconfig: Move Kconfig deps back into build/config

revert commit 1b9e740a8 (kconfig: fix failing to generate auto.conf) [1]

The above change caused all of the enabled kconfig options to be written
into the top level build directory.  We don't want that, so go back to
the old behavior for the coreboot tree.

[1] 1b9e740a81

Signed-off-by: Martin Roth <gaumless@gmail.com>
Change-Id: I2904f69a5d85337ad0a6b48590ccd4b4a6e38b70
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69536
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>

util/kconfig/confdata.c

@@ -230,6 +230,13 @@ static const char *conf_get_autoheader_name(void)
 	return name ? name : "include/generated/autoconf.h";
 }
 
+static const char *conf_get_autobase_name(void)
+{
+	char *name = getenv("KCONFIG_SPLITCONFIG");
+
+	return name ? name : "include/config/";
+}
+
 static int conf_set_sym_val(struct symbol *sym, int def, int def_flags, char *p)
 {
 	char *p2;
@@ -1024,19 +1031,14 @@ static int conf_write_autoconf_cmd(const char *autoconf_name)
 
 static int conf_touch_deps(void)
 {
-	const char *name, *tmp;
+	const char *name;
 	struct symbol *sym;
 	int res, i;
 
+	strcpy(depfile_path, conf_get_autobase_name());
+	depfile_prefix_len = strlen(depfile_path);
+
 	name = conf_get_autoconfig_name();
-	tmp = strrchr(name, '/');
-	depfile_prefix_len = tmp ? tmp - name + 1 : 0;
-	if (depfile_prefix_len + 1 > sizeof(depfile_path))
-		return -1;
-
-	strncpy(depfile_path, name, depfile_prefix_len);
-	depfile_path[depfile_prefix_len] = 0;
-
 	conf_read_simple(name, S_DEF_AUTO);
 	sym_calc_value(modules_sym);