ntb: intel: Add Icelake (gen4) support for Intel NTB

Adding 4th generation Intel NTB support bits. There are a lot of common
parts that the gen4 NTB has with gen3 NTB on Skylake. The commonalities are
reused in gen4 Icelake NTB.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

ntb: intel: Make intel_ntb3_peer_db_addr static

Fix sparse warning:

drivers/ntb/hw/intel/ntb_hw_gen3.c:535:5: warning:
symbol 'intel_ntb3_peer_db_addr' was not declared. Should it be static?

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

NTB: add new parameter to peer_db_addr() db_bit and db_data

NTB door bell usage depends on NTB hardware.

ex: intel NTB gen1 has one peer door bell register which can be controlled
by the bitmap writen to it, while Intel NTB gen3 has a registers
per door bell and the data trigering the each door bell is always 1.

therefore exposing only peer door bell address forcing the user
to be aware of such low level details

Signed-off-by: Leonid Ravich <Leonid.Ravich@emc.com>
Acked-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Acked-by: Allen Hubbe <allenbh@gmail.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

ntb: intel: change references of skx to gen3

Change all references to skx to gen3 NTB.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

ntb: intel: split out the gen3 code

Move the Intel hw gen3 code to its own source file. The ntb_hw_intel.c was
getting too large and makes it hard to maintain with future hardware
changes.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>