Which Is FPGA DMA or AGX PCIe DMA better

Video streaming data from FPGA PCIe to GPU and from GPU back to FPGA PCie using RDMA do we need the FPGA DMA or the AGX SoC PCIe DMA and which is best ?

Will the FPGA DMA operation have access to GPU memory ?

This is all a function of the driver for your FPGA. Questions about Jetson AGX should be asked on the appropriate Jetson forum.