hw/mcu/native: Allow tickless idle without min limit
hw/mcu/native: Allow tickless idle without min limit

Min limit does not make sense on simulator (and it was like this before
tickless time was configurable...).

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core