platforms: fomu: add spiflash4x definition

Fomu Hacker supports dual spi, so add a "spiflash4x" definition.
The litex spi_flash module will run this flash in dual mode, because the
`dq` array is only two signals wide.

Signed-off-by: Sean Cross <sean@xobs.io>

litex_boards/partner/platforms/fomu_hacker.py

@@ -39,6 +39,12 @@ _io = [
         Subsignal("mosi", Pins("F1"), IOStandard("LVCMOS33")),
         Subsignal("miso", Pins("E1"), IOStandard("LVCMOS33")),
     ),
+
+    ("spiflash4x", 0,
+        Subsignal("cs_n", Pins("C1"), IOStandard("LVCMOS33")),
+        Subsignal("clk",  Pins("D1"), IOStandard("LVCMOS33")),
+        Subsignal("dq",   Pins("F1 E1"), IOStandard("LVCMOS33")),
+    ),
 ]
 
 # Connectors ---------------------------------------------------------------------------------------