net/mlx4_core: Implement the master-slave communication channel

When SRIOV is enabled, pf and vfs communicate via shared comm channel.
The vf gets its side of the comm channel via a VF BAR.
Each VF (slave) creates its vHCR (virtual HCA Command Register),
Its DMA address is passed to the PF (master) using Communication Channel Register.
The same Register is used to notify the master of commands posted by the
slaves and for the master to pass events to the slaves, such as command completions
and asynchronous events.

The vHCR format is identical to the HCR format, except for the 'go' and 't' bits,
which are reserved in the vHCR. Posting commands to the vHCR is identical to
the way it is done with the HCR, albeit that the function/PF token fields are
used instead of the HCR go bit.
Specifically:
- When the function prepares a new command in the vHCR, it issues the Post_vHCR_cmd
  communication channel command and toggles the value of the function token;
  when PF token has an equal value, the command has been accepted and a new command may be posted.
- When the PF detects a Post_vHCR_cmd command, it concludes that a new command is available in the vHCR;
  after processing the command, the PF toggles the PF token to match the function token.

When the 'e' bit is not set, the completion of a Post_vHCR_cmd command also indicates
the completion the vHCR command. If, however, the 'e' bit is set, the completion of a
Post_vHCR_cmd command only indicates that the vHCR command has been accepted for execution by the PF.

Function commands are processed by the PF as follows:
-DMA (using the ACCESS_MEM command) the vHCR image into a shadow buffer.
-Validate that the opcode is non-privileged, and that the opcode- and input-modifiers are legal.
-DMA the in-box (if required) into a shadow buffer.
-Validate the command:
	o Resource ranges (e.g., QP ranges).
	o Partition key.
	o Ranges of referenced resources (e.g., CQs within QP contexts).
-If the 'e' bit is set
	o complete the Post_vHCR_cmd command
-Execute the command on the HCR.
-DMA the results to the vHCR out-box (if required).
-If the 'e' bit is set
	o Indicate command completion by generating a completion event using the GEN_EQE command
-Otherwise
	o DMA the command status to the vHCR
	o Complete the Post_vHCR_cmd command
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Yevgeny Petrillin <yevgenyp@mellanox.com>
Signed-off-by: Liran Liss <liranl@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>