haswell: Factor out `max_ddr3_freq`

All mainboards choose the maximum speed of DDR3-1600.

Change-Id: I8863f9d1df950b924f596689ebf1bfda5d317e06
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43120
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Tristan Corrick <tristan@corrick.kiwi>
Reviewed-by: Michael Niewöhner
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/northbridge/intel/haswell/romstage.c b/src/northbridge/intel/haswell/romstage.c
index 7c27827..ca94813 100644
--- a/src/northbridge/intel/haswell/romstage.c
+++ b/src/northbridge/intel/haswell/romstage.c
@@ -52,6 +52,7 @@
 		.gpiobase = DEFAULT_GPIOBASE,
 		.temp_mmio_base = 0xfed08000,
 		.tseg_size = CONFIG_SMM_TSEG_SIZE,
+		.max_ddr3_freq = 1600,
 	};
 
 	mainboard_fill_pei_data(&pei_data);