Unused address pins in AVR ATMEGA162
You can use the "Special Function IO Register - SFIOR" (bits XMM2, XMM1, XMM0) to reduce the number of address pins used by the XMEM interface.

Alternatively just leave those pins on the AVR unconnected; that should be fine because with XMEM enabled, they are outputs only. Under no circumstances should you connect them to Vcc or GND directly, otherwise a single accidental RAM access to the "wrong" RAM address could destroy the AVR.

Tie any unused address pins on the SRAM (inputs) to either Vcc or GND via a pull-up/-down resistor.