loadstore1: Complete mfspr/mtspr a cycle later

loadstore1: Complete mfspr/mtspr a cycle later

This makes mfspr and mtspr complete (and mfspr write back) on the
cycle after the instruction is received from execute1, rather than
on the same cycle.  This makes them match all other instructions
that execute in one cycle.  Because these instructions are marked
as single-issue, there wasn't the possibility of having two
instructions complete on the same cycle (which we can't cope with),
but it is better to fix this.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>