fastboot: call mke2fs tools to generate ext4 image

Set MKE2FS_CONFIG to empty to use mke2fs default configs

Test: fastboot --wipe-and-use-fbe
Bug: 35219933
Change-Id: Ibc97bb125899e1f1fe820d53709fdb2ab291c171
(cherry picked from commit d14d7c14cbe297614bf99dae9bf50b1fc342c44e)
2 files changed