create spfile

1. 如果Oracle已經startup unmount，是不能create spfile from pfile;否則會出現ORA-32002: cannot create SPFILE already being used by the instance
2. 在shutdown後，用SQL*PLUS進入，顯示Connected to an idle instance.；此時可以create spfile from pfile;
3. create pfile from spfile則隨時可以