Fix host synchronization

[pxl-th]

• Fix typo in isempty for list of active kernels.
• Move to the next kernel in the list only when done waiting on the previous kernel.
  Previously this may have led to a following sync issue:

- monitor pops kernel to wait on, moves to the next kernel and starts waiting on the pop'd kernel
- host calls AMDGPU.synchronize(), but since it is empty it returns immediately
- monitor finishes waiting on pop'd kernel

• Remove scratch alloc limiter.

[vchuravy]

Is this advisory? E.g. does the kernel run correctly if it get's less than the requested memory?

[pxl-th]

Probably not... If decreased to a too low value, kernel crashes.
I remember it was added baaack when we were dealing with HSA_STATUS_ERROR_OUT_OF_RESOURCES queue errors.
But since then there's been a lot of fixes regarding memory usage, so maybe worth removing it.

[pxl-th]

Removed. Everything works fine without it.