vboot: Add support for recovery mode with forced memory retraining

1. Add new function vboot_recovery_mode_memory_retrain that indicates if
recovery mode requires memory retraining to be performed.
2. Add helper function get_recovery_mode_retrain_switch to read memory
retrain switch. This is provided as weak function which should be
implemented by mainboard just like {get,clear}_recovery_mode_switch.

BUG=chrome-os-partner:59352
BRANCH=None
TEST=Verified behavior of recovery mode with forced memory retraining on
reef

Change-Id: I46c10fbf25bc100d9f562c36da3ac646c9dae7d1
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/17241
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/bootmode.h

@@ -22,6 +22,7 @@ int get_write_protect_state(void);
 int get_sw_write_protect_state(void);
 int get_developer_mode_switch(void);
 int get_recovery_mode_switch(void);
+int get_recovery_mode_retrain_switch(void);
 int clear_recovery_mode_switch(void);
 int get_wipeout_mode_switch(void);
 int get_lid_switch(void);

src/vboot/bootmode.c

@@ -162,6 +162,16 @@ int vboot_recovery_mode_enabled(void)
 	return !!vboot_check_recovery_request();
 }
 
+int __attribute__((weak)) get_recovery_mode_retrain_switch(void)
+{
+	return 0;
+}
+
+int vboot_recovery_mode_memory_retrain(void)
+{
+	return get_recovery_mode_retrain_switch();
+}
+
 int vboot_developer_mode_enabled(void)
 {
 	if (!IS_ENABLED(CONFIG_VBOOT))

src/vboot/vboot_common.h

@@ -107,5 +107,6 @@ void verstage_mainboard_init(void);
 /* Check boot modes */
 int vboot_developer_mode_enabled(void);
 int vboot_recovery_mode_enabled(void);
+int vboot_recovery_mode_memory_retrain(void);
 
 #endif /* __VBOOT_VBOOT_COMMON_H__ */