[avb] Verify kernel integrity against the trusted key

This implementation is only tested with glibc outside pvmfw as
it still requires some libc methods implementation in pvmfw. When
the latter is ready, we can connect pvmfw to this implementation.

Bug: 256148034
Test: atest libpvmfw_avb.test && m pvmfw_img
Change-Id: I3e6372411fdd81b6293bbd34215d650c4276af8a
diff --git a/pvmfw/avb/src/lib.rs b/pvmfw/avb/src/lib.rs
index eb1f918..1f39076 100644
--- a/pvmfw/avb/src/lib.rs
+++ b/pvmfw/avb/src/lib.rs
@@ -15,6 +15,8 @@
 //! A library implementing the payload verification for pvmfw with libavb
 
 #![cfg_attr(not(test), no_std)]
+// For usize.checked_add_signed(isize), available in Rust 1.66.0
+#![feature(mixed_integer_ops)]
 
 mod verify;