rockpi4: increase root FS size from 384 to 640M when LINUX_MODULES=y

make LINUX_MODULES=y fails due to insufficient space for the root FS.
Therefore increase the default size from 384 to 640M. With that the
available space is 35.5M:

 # df -h /
 Filesystem                Size      Used Available Use% Mounted on
 /dev/root               629.5M    562.0M     35.5M  94% /

Signed-off-by: Jerome Forissier <[email protected]>
Reviewed-by: Joakim Bech <[email protected]>

rockpi4.mk

@@ -37,7 +37,7 @@ BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV = y
 BR2_PACKAGE_IFUPDOWN_SCRIPTS = y
 BR2_SYSTEM_DHCP = eth0
 # An image with module takes more space
-BR2_TARGET_ROOTFS_EXT2_SIZE = 384M
+BR2_TARGET_ROOTFS_EXT2_SIZE = 640M
 # Enable SSH daemon for remote login
 BR2_PACKAGE_OPENSSH = y
 BR2_PACKAGE_OPENSSH_SERVER = y