src/device: Add guards on all header files

Change-Id: I8641f32ed2221f1d6e6dac884912251f64424f4d
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20737
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

src/device/oprom/include/io.h

@@ -11,6 +11,9 @@
  * GNU General Public License for more details.
  */
 
+#ifndef __OPROM_IO_H__
+#define __OPROM_IO_H__
+
 #if IS_ENABLED(CONFIG_ARCH_X86)
 #include <arch/io.h>
 #else
@@ -22,3 +25,4 @@ u8 inb(u16 port);
 u16 inw(u16 port);
 u32 inl(u16 port);
 #endif
+#endif /* __OPROM_IO_H__ */