kconfig: Allow architectures to select board specific configs

This patch introduces the framework required for architectures to supply
several independent configurations. Three architectures does this today:
ppc, ppc64 and arm.
The infrastructure provided here requires the files to be located in
the following directory:
arch/$(ARCH)/configs
The file shall be named <board>_defconfig

To select the configuration for ppc/gemini simply issue the following command:
make gemini_defconfig
This will generate a valid configuration.

ppc and ppc64 already comply to the above requirements, arm needs some
trivial updates.

scripts/kconfig/Makefile

@@ -40,6 +40,9 @@ allmodconfig: $(obj)/conf
 defconfig: $(obj)/conf
 	$< -d arch/$(ARCH)/Kconfig
 
+%_defconfig: $(obj)/conf
+	$(Q)$< -D arch/$(ARCH)/configs/$@ arch/$(ARCH)/Kconfig
+
 # Help text used by make help
 help:
 	@echo  '  oldconfig	  - Update current config utilising a line-oriented program'

scripts/kconfig/conf.c

@@ -26,6 +26,7 @@ enum {
 	set_no,
 	set_random
 } input_mode = ask_all;
+char *defconfig_file;
 
 static int indent = 1;
 static int valid_stdin = 1;
@@ -483,11 +484,12 @@ static void check_conf(struct menu *menu)
 
 int main(int ac, char **av)
 {
+	int i = 1;
 	const char *name;
 	struct stat tmpstat;
 
-	if (ac > 1 && av[1][0] == '-') {
-		switch (av[1][1]) {
+	if (ac > i && av[i][0] == '-') {
+		switch (av[i++][1]) {
 		case 'o':
 			input_mode = ask_new;
 			break;
@@ -498,6 +500,15 @@ int main(int ac, char **av)
 		case 'd':
 			input_mode = set_default;
 			break;
+		case 'D':
+			input_mode = set_default;
+			defconfig_file = av[i++];
+			if (!defconfig_file) {
+				printf("%s: No default config file specified\n",
+					av[0]);
+				exit(1);
+			}
+			break;
 		case 'n':
 			input_mode = set_no;
 			break;
@@ -516,18 +527,21 @@ int main(int ac, char **av)
 			printf("%s [-o|-s] config\n", av[0]);
 			exit(0);
 		}
-		name = av[2];
-	} else
-		name = av[1];
+	}
+  	name = av[i];
+	if (!name) {
+		printf("%s: Kconfig file missing\n", av[0]);
+	}
 	conf_parse(name);
 	//zconfdump(stdout);
 	switch (input_mode) {
 	case set_default:
-		name = conf_get_default_confname();
-		if (conf_read(name)) {
+		if (!defconfig_file)
+			defconfig_file = conf_get_default_confname();
+		if (conf_read(defconfig_file)) {
 			printf("***\n"
 				"*** Can't find default configuration \"%s\"!\n"
-				"***\n", name);
+				"***\n", defconfig_file);
 			exit(1);
 		}
 		break;