build: add support for enabling the rootfs/boot partition size option via target feature

Signed-off-by: Felix Fietkau <nbd@nbd.name>

config/Config-images.in

@@ -268,12 +268,12 @@ menu "Target Images"
 
 	config TARGET_KERNEL_PARTSIZE
 		int "Kernel partition size (in MB)"
-		depends on GRUB_IMAGES
+		depends on GRUB_IMAGES || USES_BOOT_PART
 		default 16
 
 	config TARGET_ROOTFS_PARTSIZE
 		int "Root filesystem partition size (in MB)"
-		depends on GRUB_IMAGES || TARGET_ROOTFS_EXT4FS || TARGET_rb532 || TARGET_mvebu || TARGET_uml
+		depends on GRUB_IMAGES || USES_ROOTFS_PART || TARGET_ROOTFS_EXT4FS || TARGET_rb532 || TARGET_mvebu || TARGET_uml
 		default 256
 		help
 		  Select the root filesystem partition size.

scripts/target-metadata.pl

@@ -40,6 +40,8 @@ sub target_config_features(@) {
 		/^small_flash$/ and $ret .= "\tselect SMALL_FLASH\n";
 		/^nand$/ and $ret .= "\tselect NAND_SUPPORT\n";
 		/^virtio$/ and $ret .= "\tselect VIRTIO_SUPPORT\n";
+		/^rootfs-part$/ and $ret .= "\tselect USES_ROOTFS_PART\n";
+		/^boot-part$/ and $ret .= "\tselect USES_BOOT_PART\n";
 	}
 	return $ret;
 }

target/Config.in

@@ -96,6 +96,12 @@ config ARCH_64BIT
 config VIRTIO_SUPPORT
 	bool
 
+config USES_ROOTFS_PART
+	bool
+
+config USES_BOOT_PART
+	bool
+
 # Architecture selection
 
 config aarch64