remoteproc:core: Allow user to use ioremap to map firmware memory

This is required as a workaround as the memory used by rproc is not
contiguous. Use RPROC_CARVEOUT_USE_IOREMAP to determine if such workaround
is required of not.

Signed-off-by: Jason Wu <j.wu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>