Fixes SCP wakeup latency

When an SCP syscall completes on a CG core, which ultimately wakes up
the process, the SCP was not running until the next ksched timer tick.

This scenario could happen if an SCP blocks on a read on a pipe that
gets written to by an MCP.  The pipe write wakes the reader, and since
the kthread code is primitive, it just finishes the bottom half of the
syscall on the MCPs core (a CG core).  Core 0 could have been halted the
entire time, and had no reason to wake up.  It may have called
cpu_bored() a long time ago and has not woken up yet.

Btw, note that syscalls in the trace are written in the order of
*completion*, not submission.  This is more clear from the TSC
timestamp, but the pretty output only has msec granularity.