Partition support for FAT file system

[Frank Pagliughi <fpagliughi@mindspring.com>]

It appears that the FAT file system in eCos works if the "whole disk" is 
a single partition, meaning that the FAT Boot Sector is written into the 
MBR at sector zero. But if the disk uses a partition table in the MBR, 
then the code doesn't understand it, rejects the disk as non-FAT, and 
fails the mount. This happens even if the disk contains only a single 
partition.

I guess a quick enhancement would be for fatfs_mount() or fatfs_init() 
to check the partition table, see if there's at least one entry, and 
mount the first one it finds. If there are no partition entries, *then* 
check if the MBR is a valid FAT boot sector. This would make most disks 
(and compact flash cards) at least partially useful, rather than being 
rejected out right.

As a longer term enhancement, supporting multiple partitions would be 
nice, but ideas on how to resolve the devs/mtab idea of a disk to 
different partitions would be appreciated.

- Frank