device: introduce per device dma_pfn_offset

On few architectures, there are few restrictions on DMAble area of system
RAM. That also means that devices needs to know about this restrictions so
that the dma_masks can be updated accordingly and dma address translation
helpers can add/subtract the dma offset.

In most of cases DMA addresses can be performed using offset value of
Bus address space relatively to physical address space as following:

PFN->DMA:  __pfn_to_phys(pfn + [-]dma_pfn_offset)
DMA->PFN:  __phys_to_pfn(dma_addr) + [-]dma_pfn_offset

So we introduce per device dma_pfn_offset which can be popullated
by architecture init code while creating the devices.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Olof Johansson <olof@lixom.net>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

include/linux/device.h

@@ -691,6 +691,7 @@ struct acpi_dev_node {
  * @coherent_dma_mask: Like dma_mask, but for alloc_coherent mapping as not all
  * 		hardware supports 64-bit addresses for consistent allocations
  * 		such descriptors.
+ * @dma_pfn_offset: offset of DMA memory range relatively of RAM
  * @dma_parms:	A low level driver may set these to teach IOMMU code about
  * 		segment limitations.
  * @dma_pools:	Dma pools (if dma'ble device).
@@ -756,6 +757,7 @@ struct device {
 					     not all hardware supports
 					     64 bit addresses for consistent
 					     allocations such descriptors. */
+	unsigned long	dma_pfn_offset;
 
 	struct device_dma_parameters *dma_parms;