ACPI: Correct asl_compiler_revision value

Change-Id: I91b54b43c8bb5cb17ff86a6d9afa95f265ee49df
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/31431
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/include/version.h

@@ -27,4 +27,7 @@ struct bcd_date {
 
 extern const struct bcd_date coreboot_build_date;
 
+/* IASL version */
+extern const unsigned int asl_revision;
+
 #endif /* VERSION_H */