PCI: brcmstb: Add dma-range mapping for inbound traffic

The Broadcom STB PCIe host controller is intimately related to the
memory subsystem.  This close relationship adds complexity to how cpu
system memory is mapped to PCIe memory.  Ideally, this mapping is an
identity mapping, or an identity mapping off by a constant.  Not so in
this case.

Consider the Broadcom reference board BCM97445LCC_4X8 which has 6 GB
of system memory.  Here is how the PCIe controller maps the
system memory to PCIe memory:

  memc0-a@[        0....3fffffff] <=> pci@[        0....3fffffff]
  memc0-b@[100000000...13fffffff] <=> pci@[ 40000000....7fffffff]
  memc1-a@[ 40000000....7fffffff] <=> pci@[ 80000000....bfffffff]
  memc1-b@[300000000...33fffffff] <=> pci@[ c0000000....ffffffff]
  memc2-a@[ 80000000....bfffffff] <=> pci@[100000000...13fffffff]
  memc2-b@[c00000000...c3fffffff] <=> pci@[140000000...17fffffff]

Although there are some "gaps" that can be added between the
individual mappings by software, the permutation of memory regions for
the most part is fixed by HW.  The solution of having something close
to an identity mapping is not possible.

The idea behind this HW design is that the same PCIe module can
act as an RC or EP, and if it acts as an EP it concatenates all
of system memory into a BAR so anything can be accessed.  Unfortunately,
when the PCIe block is in the role of an RC it also presents this
"BAR" to downstream PCIe devices, rather than offering an identity map
between its system memory and PCIe space.

Suppose that an endpoint driver allocs some DMA memory.  Suppose this
memory is located at 0x6000_0000, which is in the middle of memc1-a.
The driver wants a dma_addr_t value that it can pass on to the EP to
use.  Without doing any custom mapping, the EP will use this value for
DMA: the driver will get a dma_addr_t equal to 0x6000_0000.  But this
won't work; the device needs a dma_addr_t that reflects the PCIe space
address, namely 0xa000_0000.

So, essentially the solution to this problem must modify the
dma_addr_t returned by the DMA routines routines.  There are two
ways (I know of) of doing this:

(a) overriding/redefining the dma_to_phys() and phys_to_dma() calls
that are used by the dma_ops routines.  This is the approach of

	arch/mips/cavium-octeon/dma-octeon.c

In ARM and ARM64 these two routines are defiend in asm/dma-mapping.h
as static inline functions.

(b) Subscribe to a notifier that notifies when a device is added to a
bus.  When this happens, set_dma_ops() can be called for the device.
This method is mentioned in:

    http://lxr.free-electrons.com/source/drivers/of/platform.c?v=3.16#L152



where it says as a comment

    "In case if platform code need to use own special DMA
    configuration, it can use Platform bus notifier and
    handle BUS_NOTIFY_ADD_DEVICE event to fix up DMA
    configuration."

Solution (b) is what this commit does.  It uses its own set of
dma_ops which are wrappers around the arch_dma_ops.  The
wrappers translate the dma addresses before/after invoking
the arch_dma_ops, as appropriate.

Signed-off-by: Jim Quinlan <jim2101024@gmail.com>