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/cpu/ti/am335x/header.c

@@ -12,7 +12,6 @@
  * GNU General Public License for more details.
  */
 
-#include <config.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <symbols.h>

src/cpu/ti/am335x/pinmux.c

@@ -16,7 +16,6 @@
 #include "pinmux.h"
 
 #include <arch/io.h>
-#include <config.h>
 
 static struct am335x_pinmux_regs *regs =
 	(struct am335x_pinmux_regs *)(uintptr_t)AM335X_PINMUX_REG_ADDR;

src/cpu/ti/am335x/uart.c

@@ -13,7 +13,6 @@
  */
 
 #include <stdlib.h>
-#include <config.h>
 #include <types.h>
 #include <console/uart.h>
 #include <arch/io.h>