Add 64KB romchip chip size

Add 64KB romchip chip size

This is handy for bifferboard to provide same size as original bootloader.

Change-Id: I179917d8c6354fa55cebdd70918a96cd299c4f3c
Signed-off-by: Rudolf Marek <r.marek@assembler.cz>
Reviewed-on: http://review.coreboot.org/809
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>