Explicitly set EROFS compression parameter

OTA will need to know the compression parameter used to construct EROFS
images. Currently, mkfs.erofs uses lz4hc,9 if the user didn't specify
one. But mkfs's default behavior is subject to change in future
versions. Therefore, explicitly specify the compression parameters so
OTA tooling can properly encode/decode erofs images.

Test: th
Change-Id: Ibbf67502827ee79437b766349be289048e685759