Add support for AU Mitsubish Heavy split systems

Models:
SRK20ZSA-W,
SRK25ZSA-W,
SRK35ZSA-W,
SRK50ZSA-W

Modes:
      "heat_cool",
      "cool",
      "heat",
      "dry",
      "fan_only"

Tested with SRK20ZSA-W and SRK25ZSA-W. Rest of the remotes should be exactly the same.