litedram: Update to new LiteX/LiteDRAM version

Things have changed a bit in upstream LiteX. LiteDRAM now exposes a
wishbone for the CSRs for example.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

include/console.h

@@ -6,4 +6,7 @@ void potato_uart_irq_dis(void);
 int getchar(void);
 int putchar(int c);
 int puts(const char *str);
+
+#ifndef __USE_LIBC
 size_t strlen(const char *s);
+#endif