* mcommit represents that a mem inst is retired,
lsu can write dcache / move lsroq tailptr
* mcommit uses the same datapath as scommit

EMU: print seed value before return

Uart: print to stdout

Log buffer

* this helps to seperate the message printed by emu from the logs in
  chisel

* printf() in chisel will finally output to stderr. Using a buffer will
  improve performance while redirecting stderr to a file.
* If log is enabled for every cycle, this can speed up 2X for simulation.

Impl floating point load/store

Dev bpu pipeline rebase

DecodeStage: fix bug of DecodeStage and Ibuffer

fix bug that DecodeStage could handle the sync between Brq and
DecodeBuffer

Makefile: optimize SEED generation