remoteproc: Add handler to convert virtual addr to physical addr

This is required because it is not able to get the physical from a dma
virtual address in arm64.

Singed-off-by: Wendy Liang <wendy.liang@xilinx.com>
Signed-off-by: Jason Wu <j.wu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>