Changeset 696ee75 in umon

FAT fs changes: FAT code and larger ROM size

. add fatfs umon cli to it. unmodified from the umon 1.19

distribution, apache-licensed.

. also add dosfs from the umon 1.19 distribution, which is

similarly liberally licensed.

. increase available 'ROM' size to 128kB minus

1kB secure + 18kB reserved (numbers from uboot wiki).

. no unaligned access - needed to access fields in

on-disk structs without gcc generating unaligned
access instructions (causes data abort exceptions)

. turn on shellvars for BBB as they are needed to

connect FATFS to the SD i/o functions