scause: add missing LoadMisaligned

See table 4.2 in privileged spec version 20211203 as found today at
https://riscv.org/technical/specifications/

src/register/scause.rs

@@ -34,6 +34,7 @@ pub enum Exception {
     InstructionFault,
     IllegalInstruction,
     Breakpoint,
+    LoadMisaligned,
     LoadFault,
     StoreMisaligned,
     StoreFault,
@@ -67,6 +68,7 @@ impl Exception {
             1 => Exception::InstructionFault,
             2 => Exception::IllegalInstruction,
             3 => Exception::Breakpoint,
+            4 => Exception::LoadMisaligned,
             5 => Exception::LoadFault,
             6 => Exception::StoreMisaligned,
             7 => Exception::StoreFault,
@@ -145,6 +147,7 @@ pub unsafe fn set(cause: Trap) {
             Exception::InstructionFault => 1,
             Exception::IllegalInstruction => 2,
             Exception::Breakpoint => 3,
+            Exception::LoadMisaligned => 4,
             Exception::LoadFault => 5,
             Exception::StoreMisaligned => 6,
             Exception::StoreFault => 7,