16k: Switch AOSP shusky 16k targets to use ext4 for RW filesystem am: 54e593d3e7 am: b3533149e7

Original change: https://android-review.googlesource.com/c/device/google/shusky/+/3287856

Change-Id: Ibb4a2936eb001015a7185ba3f2b159cf25ea7f1b
Signed-off-by: Automerger Merge Worker <[email protected]>