fix MmAllocateContiguous, implement polling AHCI driver.

code/hal/hal_timer.c

@@ -39,7 +39,15 @@ static uint64_t QueryTicks(void) { return gTicks; }
 static void Stall(uint32_t us) {
     uint64_t start = gTicks;
     uint64_t ms    = (us + 999) / 1000;
-    while ((gTicks - start) < ms) _mm_pause();
+
+    // Spin up to 100ms worth of IO delays waiting for ticks to advance.
+    // If gTicks doesn't move (interrupts off), fall back to pure IO delay.
+    uint32_t io_iters = (uint32_t)(ms * 1000);
+    for (uint32_t i = 0; i < io_iters; i++) {
+        if ((gTicks - start) >= ms) return;   // interrupt-driven path
+        __outbyte(0x80, 0);
+    }
+    // If we exhausted the IO delay loop we've waited long enough anyway.
 }
 
 // Returns HPET ticks/second, or 0 if HPET is unavailable.