lpmake: Fix some issues in size calculation.

When using "auto" for the super partition size, the size was computed
totally wrong for small alignments. It doesn't show up in production
since the default alignment is quite large (1MiB).

Also, when specifing image files, the partition size is now
automatically calculated if specified as 0.

Bug: N/A
Test: lpmake
Change-Id: I8f3f3ff2d5f0b60163c17edc4bdba647fa1decc1
1 file changed