[lwp][rv64] restore tp register in arch_thread_signal_enter to fix user-mode memory access

components/lwp/arch/risc-v/rv64/lwp_gcc.S

@@ -178,6 +178,9 @@ arch_thread_signal_enter:
     /* restore user GP */
     LOAD gp, FRAME_OFF_GP(s3)
 
+    /* restore user TP */
+    LOAD tp, FRAME_OFF_TP(s3)
+
     /**
      * handler(signo, psi, ucontext);
      */

libcpu/risc-v/common64/stackframe.h

@@ -41,6 +41,7 @@
 #define FRAME_OFF_SSTATUS   BYTES(2)
 #define FRAME_OFF_SP        BYTES(32)
 #define FRAME_OFF_GP        BYTES(3)
+#define FRAME_OFF_TP        BYTES(4)
 
 /* switch frame */
 #define RT_HW_SWITCH_CONTEXT_SSTATUS    0