Add De Bruijn LUT for future O(1) priority selection

Prepare for O(1) bitmap index lookup by adding a 32-entry De Bruijn
sequence table. The table will be used in later commits to replace
iterative bit scanning. No functional change in this patch.

Author: vicLin8712

kernel/task.c

@@ -330,6 +330,11 @@ void panic(int32_t ecode)
     hal_panic();
 }
 
+/* RISC-V optimized priority finding using De Bruijn sequence */
+static const uint8_t debruijn_lut[32] = {
+    0,  1,  28, 2,  29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4,  8,
+    31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6,  11, 5,  10, 9};
+
 /* Weak aliases for context switching functions. */
 void dispatch(void);
 void yield(void);