Which android devices have optimized encryption hardware?
Fundamentally Android requires the developer to implement encryption directly (ie, there is no OS supplied framework for this).

To the best of my knowledge, there is no current Android hardware with Encryption built into to the hardware.  The new "Black Phone" that Boeing is reportedly making for the US defense industry is likely an exception to this (the phone HW was specifically engineered for security).

Basically iOS is encrypted by default, and Android requires the devloper to implement encryption in their applications.