ASRock E350M1: mainboard.c: Include `cimx_util.h` for `pm_iowrite`

When building the ASRock E350M1, the following warning is shown.

    $ make # on Jenkins (build server)
    […]
        CC         mainboard/asrock/e350m1/mainboard.ramstage.o
    src/mainboard/asrock/e350m1/mainboard.c: In function 'mainboard_enable':
    src/mainboard/asrock/e350m1/mainboard.c:63:2: warning: implicit declaration of function 'pm_iowrite' [-Wimplicit-function-declaration]
    […]

This warning was introduced by moving the initialization of the
ASF registers using `pm_iowrite` to `mainboard.c` in

    commit db6c5bfd8b
    Author: Jens Rottmann <JRottmann@LiPPERTembedded.de>
    Date:   Thu Mar 21 22:21:28 2013 +0100

        Asrock E350M1: Use SPD read code from F14 wrapper

        Reviewed-on: http://review.coreboot.org/2875

and is fixed by including `southbridge/amd/cimx/cimx_util.h`
declaring `pm_iowrite`.

Note, that the other AMD SB800 based boards seem to use the
header file `southbridge/amd/sb800/sb800.h`, so no warning is shown
for those. But since the CIMx SB800 code is used, the routines
from the CIMx directory are more appropriate to declare these functions.

So delete the commented out include line for this header too.

Change-Id: I179aad5157c5a91294339a3e7b6c4c1715c6f099
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/2957
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/asrock/e350m1/mainboard.c

@@ -24,7 +24,7 @@
 #include <cpu/x86/msr.h>
 #include <cpu/amd/mtrr.h>
 #include <device/pci_def.h>
-//#include <southbridge/amd/sb800/sb800.h>
+#include <southbridge/amd/cimx/cimx_util.h>
 
 //#define SMBUS_IO_BASE 0x6000
 void set_pcie_reset(void);