mb/siemens/mc_ehl3: Use device/mmio.h instead of device/pci_ops.h

The {read,write}{16,32}() functions used in this file come from the
mmio.h header, so include it directly.

BUG=none
TEST=Read out the SD card controller (device 1a.1) PCI registers
in Linux and check whether the values reflect the ones defined
in this file.

Change-Id: Iff7b55ef2bf98371b7d7d9114ccf3ebed64772a2
Signed-off-by: Jan Samek <jan.samek@siemens.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72009
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

src/mainboard/siemens/mc_ehl/variants/mc_ehl3/mainboard.c

@@ -2,7 +2,7 @@
 
 #include <baseboard/variants.h>
 #include <bootstate.h>
-#include <device/pci_ops.h>
+#include <device/mmio.h>
 #include <gpio.h>
 #include <soc/pci_devs.h>