1. Bcache block with high mem address is after lower mem address in RCU list when initing bcache.
2. Format will clear the bcache before writing the FAT.
3. The fatfs_readdir use the bcache writing block to reduce the chance of data switching out
4. Add performance analysing macron switch

Change-Id: I8fbc48418509d2e660d725d2c265266e931c26f8