Allow 64-bit Mcause::from_bits on rv64

Fixes #333

Author: jsgf

riscv/CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+- Allow all bits to be set in Mcause::from_bits on 64-bit targets.
+
 ## [v0.14.0] - 2025-06-10
 
 ### Added

riscv/src/register/mcause.rs

@@ -5,7 +5,7 @@ pub use crate::interrupt::Trap;
 read_only_csr! {
     /// `mcause` register
     Mcause: 0x342,
-    mask: 0xffff_ffff,
+    mask: usize::MAX,
 }
 
 #[cfg(target_arch = "riscv32")]