elog: Allow calling boot_count_read() without CONFIG_ELOG_BOOT_COUNT

Have boot_count_read() just return 0 if CONFIG_ELOG_BOOT_COUNT is not
enabled.

BUG=b:79865267
TEST=firmware_EventLog

Change-Id: I70f16226371324dea37b3f36f85c2037e324ef31
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-on: https://review.coreboot.org/26526
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/include/elog.h b/src/include/elog.h
index 0f6a811..0776c36 100644
--- a/src/include/elog.h
+++ b/src/include/elog.h
@@ -250,7 +250,14 @@
 
 extern u32 gsmi_exec(u8 command, u32 *param);
 
+#if IS_ENABLED(CONFIG_ELOG_BOOT_COUNT)
 u32 boot_count_read(void);
+#else
+static inline u32 boot_count_read(void)
+{
+	return 0;
+}
+#endif
 u32 boot_count_increment(void);
 
 /*