calculation partition size use compressed image size

If dynamic partitioning is enabled and the partition size is not set,
du will be used to calculate the partition size.

For compressed file systems, it's better to use the compressed size
to avoid wasting space.

Bug:174816929
Test: erofs image size is smaller than the original file
Change-Id: I1deda85d312c19620680531223fffcfb815e5fd4
Signed-off-by: Huang Jianan <huangjianan@oppo.com>