Add --keep_memtag_mode for --wipe_data

This allows us to erase the system image without resetting the MTE
state. This is useful for TestHarness looking to re-use an MTE enabled
device without incurring an extra reboot to re-enable after reboot.

Bug: 300694575
Change-Id: Ie1ea6891361e561189b9390b97b0b4a4c3a6d7e8