Declare get_write_protect_state() without ChromeOS

Change-Id: I72471ac68088cd26f8277b27b75b7d44ad72cfc4
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/5642
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/include/bootmode.h

@@ -22,6 +22,7 @@
 
 /* functions implemented per mainboard: */
 void init_bootmode_straps(void);
+int get_write_protect_state(void);
 int get_developer_mode_switch(void);
 int get_recovery_mode_switch(void);