soc_sdram: don't generate sdram initialization error message when integrated_main_ram is used

litex/soc/integration/soc_sdram.py

@@ -41,6 +41,7 @@ class SoCSDRAM(SoCCore):
 
     def __init__(self, platform, clk_freq, l2_size=8192, **kwargs):
         SoCCore.__init__(self, platform, clk_freq, **kwargs)
+        if not self.integrated_main_ram_size:
             if self.cpu_type is not None and self.csr_data_width != 8:
                  raise NotImplementedError("BIOS supports SDRAM initialization only for csr_data_width=8")
         self.l2_size = l2_size