Add support for specifying erofs blocksize

This change allows us to specify erofs filesystem block size
which will be used to create erofs image.

Either it can be specified at board level using
BOARD_EROFS_BLOCKSIZE. Or per read only partition image
using BOARD_<PARTITION>IMAGE_EROFS_BLOCKSIZE.

Examples:
BOARD_EROFS_BLOCKSIZE := 16384 OR
BOARD_PRODUCTIMAGE_EROFS_BLOCKSIZE := 16384

Bug: 303316443
Test: m and file ${ANDROID_PRODUCT_OUT}/*.img

Change-Id: I9bf3d299ae02165d0bffc62f474a302408d8b9b9
Signed-off-by: Sandeep Dhavale <dhavale@google.com>