Kernel/IPC: Add a small delay after each SyncRequest to prevent thread starvation.

Ported from citra PR #3091

The delay specified here is from a Nintendo 3DS, and should be measured in a Nintendo Switch.

This change is enough to prevent Puyo Puyo Tetris's main thread starvation.

src/core/hle/kernel/thread.h

@@ -40,6 +40,7 @@ enum ThreadStatus {
     THREADSTATUS_READY,          ///< Ready to run
     THREADSTATUS_WAIT_ARB,       ///< Waiting on an address arbiter
     THREADSTATUS_WAIT_SLEEP,     ///< Waiting due to a SleepThread SVC
+    THREADSTATUS_WAIT_IPC,       ///< Waiting for the reply from an IPC request
     THREADSTATUS_WAIT_SYNCH_ANY, ///< Waiting due to WaitSynch1 or WaitSynchN with wait_all = false
     THREADSTATUS_WAIT_SYNCH_ALL, ///< Waiting due to WaitSynchronizationN with wait_all = true
     THREADSTATUS_DORMANT,        ///< Created but not yet made ready