Add pcluster and deduplication support for erofs images.

This adds BOARD_xIMAGE_EROFS_PCLUSTER_SIZE and
BOARD_EROFS_PCLUSTER_SIZE, which set the "pcluster size" of erofs images
for individual images or all erofs images respectively. The pcluster
size affects the maximum size of a physical compressed block.

This also adds BOARD_EROFS_SHARE_DUP_BLOCKS, which turns on chunk
support in EROFS.

Bug: 201685920
Test: manual test
Change-Id: I27ec0899f89890562796dd9fa567fc74182fbefb