PIC32 USB mass storage device works; USB and MSC are now enabled by default in...

PIC32 USB mass storage device works; USB and MSC are now enabled by default in the PIC32MX7 MMB configuration

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@4801 42af7a65-404d-4744-a932-0658087f49c3