AFAIK NuttX doesn't have support to Serial SRAM yet. At least I never see a driver to it. Normally people use real SDRAM chips controlled by FMSC (in the case of STM32). It should be a nice addition if you create a driver for Serial SRAM.
You can't use serial SRAM from a framebuffer, however. If that is the intent. (It would have to be bigger as well).
Serial SRAM cannot be randomly accessed like normal memory. QSPI is an option, perhaps, if you configure it to support random access. Regular FSMC SRAM on an STM32F4-Discovery daughterboard would be easier than either of those options.
