STM32 - 2 MegaByte DMA Transfer ADC To SDRAM
To answer the first question, yes, you can. You'll have to use multiple DMA operations, and most DMA controllers have some means of "chaining" operations together for continuous operation. I don't have the specific details about how that works on the STM32. The CPU will probably have to process an interrupt at the end of each DMA block.

To answer the second question, it's probably a confusion in terminology. The word "bank" is being used in one sense regarding how the SDRAM is organized internally, but in a completely different sense regarding how the SDM32 addresses memory in general. Banks on the CPU do not correspond to banks inside the SDRAM. As far as the CPU is concerned, the entire SDRAM chip is one big bank.