i40e: Ioremap changes

For future device support we do not want to map the whole CSR space since some
of it is mapped by other drivers with different mapping methods.

Note: As a side effect, the flash region (if exposed through the memory map)
gets unmapped too since it follows the future use region.

Change-ID: Ic729a2eacd692984220b1a415ff4fa0f98ea419a
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>