Revert "Revert "zcache-main: switch to lz4 as default""

This reverts commit 937dd68ea44e31ac4bbe8640bf09c1a1de202813.
Revert "Revert "zram_drv: switch default compressor to new lz4""

This reverts commit 3d4f7c977b941f479909fef5d362d1a7ebb75d35.