Make MRC vs native a config rather than making a separate chipset for it.

Tested by making lenovo x230 configurable despite pretty MRC bugs.

Change-Id: Ia2a123f24334f5cd5f42473b7ce7f3d77c0e65b7
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: https://review.coreboot.org/13658
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/google/parrot/devicetree.cb

@@ -18,6 +18,8 @@ chip northbridge/intel/sandybridge
 	register "gpu_cpu_backlight" = "0x000001d4"
 	register "gpu_pch_backlight" = "0x03aa0000"
 
+	register "max_mem_clock_mhz" = "666"
+
 	device cpu_cluster 0 on
 		chip cpu/intel/socket_rPGA989
 			device lapic 0 on end