Move BOARD_EXT4_SHARE_DUP_BLOCKS to BoardConfigMainlineCommon.mk

BOARD_EXT4_SHARE_DUP_BLOCKS can reduce the image size. Move it to
BoardConfigMainlineCommon.mk to apply on all mainline based
targets.

Bug: 155589918
Test: build aosp_arm-userdebug
Test: build gsi_gms_arm64-userdebug
Test: build sdk_gphone_arm64-userdebug
Change-Id: I8c4c7c9b2982daf6bf02991b4e62a43b296d003e