mimir: Skip clearHalt to fix Volla Tablet bootloader unlock

Proactive clearHalt on USB open() breaks the Volla Tablet (MediaTek)
bootloader — flashing unlock never receives a response. Add a
skip_clear_halt config flag in device JSON that disables clearHalt
during transport open for devices where it causes issues. Set it
for mimir (Volla Tablet).

Signed-off-by: Jackeagle <jackeagle102@gmail.com>