x86: revert default root size back to 256 MB

2 GB is overkill and was only added to allow unlimited ext4 resizing,
which is a pretty rare use case. 256 MB allows resizing up to 256 GB,
which should be good enough for almost all users.

A lot of this is mostly irrelevant anyway, since you can just use
squashfs + ext4 overlay.

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

config/Config-images.in

@@ -253,8 +253,7 @@ menu "Target Images"
 	config TARGET_ROOTFS_PARTSIZE
 		int "Root filesystem partition size (in MB)"
 		depends on GRUB_IMAGES || TARGET_ROOTFS_EXT4FS || TARGET_rb532 || TARGET_mvebu || TARGET_uml
-		default 2048 if TARGET_x86
+		default 256
-		default 256 if ! TARGET_x86
 		help
 		  Select the root filesystem partition size.