* Miniconfig: change dtlb size to 32 at minimal config

* mmu.dtlb: change tlb's replacement access code style

dtlb now can support plru (functionaly).
plru with multi-access is chained, so there will be long latency
  for dtlb to use plru.

* mmu.tlb: add tlb at new level named btlb

bridge tlb:
one l0-tlb in each mem pipeline
all the l0-tlb connect to bridge tlb
btlb connects to l2tlb, so btlb is also l1-tlb
itlb remains the same

* mmu.tlb: set tlb size: l0-8, l1-64

* mmu.btlb: add sfence logic

* mmu.tlb: fix bug of sfence logic of g bit

* mmu.btlb: add some perf counter

* mmu.btlb: fix bug of random replace

* mmu.filter: add port vector to record which ports the reqs come from

* mmu.btlb: add some perf counter && add refill mask

* mmu.filter: add check for flushed req