ffspart: broken layout when blocksize is larger than first partition start

[shenki]

Creating a ffs image with this configuration:

@0,0x0,
FIRST,0x400,0x100,,,/dev/zero

$ touch test.ffs
$ ./ffspart -s 0x1000 -c 10 -i test.csv -p test.ffs
$ pflash -i -F test.ffs 
Flash info:
-----------
Name          = /home/joel/dev/skiboot/external/ffspart/test.ffs
Total size    = 0MB	 Flags E:ECC, P:PRESERVED, R:READONLY, B:BACKUP
Erase granule =  0KB           F:REPROVISION, V:VOLATILE, C:CLEARECC

TOC@0x00000000 Partitions:
-----------
ID=00            part 0x00000000..0x00001000 (actual=0x00001000) [----------]
ID=01           FIRST 0x00000000..0x00000000 (actual=0x00000100) [----------]

FIRST should start at 0x400, but as eraseblock size 0x1000 > 0x400, the toc (named 'part') is placed there first, and everything is broken from then on.

While it's a bad idea to have any partition smaller than the eraseblock size, ffspart should still create the image, and perhaps warn the user when creating the partition boundry when it is not eraseblock aligned.