icache: Do PLRU update one cycle later

icache: Do PLRU update one cycle later

This does the PLRU update based on r.hit_valid and r.hit_way rather
than req_is_hit and req_hit_way, which means there is now a register
between the TLB and cache tag lookup and the PLRU update, which
should help with timing.

As a result, the PLRU victim way selection becomes valid one cycle
later, in the cycle when r.state = CLR_TAG.  So we have to use the
PLRU output directly in the CLR_TAG state and r.store_way in the
WAIT_ACK state.

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