generic: increase RootFS size when GLUON_DEBUG is enabled

This increases the size of the root filesystem when GLUON_DEBUG is
enabled. Otherwise, the filesystem is too small.

Closes #1907

targets/generic

@@ -54,6 +54,7 @@ end
 if envtrue.GLUON_DEBUG then
 	config 'CONFIG_DEBUG=y'
 	config 'CONFIG_NO_STRIP=y'
+	config 'CONFIG_TARGET_ROOTFS_PARTSIZE=500'
 	config '# CONFIG_USE_STRIP is not set'
 	config '# CONFIG_USE_SSTRIP is not set'
 end