Merged fs0 to mm0 for simpler progress on posix api.

mm0 and all other posix dependents are building ok.

conts/posix/mm0/fs/bdev.c

@@ -0,0 +1,15 @@
+/*
+ * This is just to allocate some memory as a block device.
+ */
+#include <l4/macros.h>
+#include <memfs/memfs.h>
+
+extern char _start_bdev[];
+extern char _end_bdev[];
+
+__attribute__((section(".data.memfs"))) char blockdevice[MEMFS_TOTAL_SIZE];
+
+void *vfs_rootdev_open(void)
+{
+	return (void *)_start_bdev;
+}