Bracket SGPIO GPDMA slice configuration with multislice==false test. It only makes sense in single slice mode (until I have a clever idea for doing GPDMA with multiple slices).

firmware/common/sgpio.c

@@ -228,6 +228,7 @@ void sgpio_configure(
 		slice_enable_mask |= (1 << slice_index);
 	}
 
+	if( multi_slice == false ) {
 		SGPIO_MUX_CFG(slice_gpdma) =
 			  SGPIO_MUX_CFG_CONCAT_ORDER(0) /* Self-loop */
 			| SGPIO_MUX_CFG_CONCAT_ENABLE(1)
@@ -259,6 +260,7 @@ void sgpio_configure(
 		SGPIO_REG_SS(slice_gpdma) = 0x77777777;  // Shadow output data register, LSB -> out1
 		
 		slice_enable_mask |= (1 << slice_gpdma);
+	}
 		
 	// Start SGPIO operation by enabling slice clocks.
 	SGPIO_CTRL_ENABLE = slice_enable_mask;