buildsystem: Drop explicit (k)config.h includes

We have kconfig.h auto-included and it pulls config.h too.

Change-Id: I665a0a168b0d4d3b8f3a27203827b542769988da
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/17655
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)

src/device/pci_device.c

@@ -47,7 +47,6 @@
 #include <device/pciexp.h>
 #include <device/hypertransport.h>
 #include <pc80/i8259.h>
-#include <kconfig.h>
 #include <vboot/vbnv.h>
 
 u8 pci_moving_config8(struct device *dev, unsigned int reg)