traps/interrupts: Refactor trap handling and align CSR access

src/kernel/interrupts.h

@@ -3,6 +3,8 @@
 
 #define MSTATUS 0x300
 #define MIE 0x304
+#define MCAUSE 0x342
+#define MEPC 0x341
 #define MSTATUS_BIT_MIE 3
 #define MIE_BIT_MTIE 7
 #define MIE_BIT_MEIE 11
@@ -56,8 +58,10 @@ typedef struct {
     uint64_t t5;      // x30
     uint64_t t6;      // x31
 
-    // Control and Status Register state
-    uint64_t mepc;    // offset 240 (Saved in traps.S)
+    // Control and Status Register state (Saved in traps.S)
+    uint64_t mepc;    // offset 240 
+    uint64_t mcause;  // offset 248
+    uint64_t mstatus; // offset 256
 } trap_frame_t;
 
 void interrupt_init();