i2c: axxia: use auto cmd for last message

i2c: axxia: use auto cmd for last message

Some recent commits to this driver were trying to make sure the TSS
interrupt is not generated on busy system due to 25ms timer expiring
between commands. It can still happen, however if STOP command is not
issued on time at the end of the transmission. If wait_for_completion in
axxia_i2c_xfer_msg() would not return after 25ms of getting an
interrupt, TSS will be generated and idev->err_msg will be set to
-ETIMEDOUT which will be returned from the axxia_i2c_xfer_msg(), even
though the transfer did actually succeed (STOP is automatically issued
when TSS triggers).

Fortunately, apart from already used manual and sequence commands, the
controller also has so called auto command. It works just like manual
mode but it but an automatic STOP is issued when either transfer length
is met or NAK is received from slave device.

This patch changes the axxia_i2c_xfer_msg() function so that auto
command is used for last message in transaction letting hardware manage
issuing STOP. TSS is disabled just after command transferring last
message finishes. Auto command, just like sequence, ends with SS
interrupt instead of SNS so handling of both had to be unified.

The axxia_i2c_stop() is no longer needed as the transfer can only end
with following conditions:
- fully successful - then last message was send by AUTO command and STOP
  was issued automatically
- NAK received - STOP is issued automatically by controller
- arbitration lost - STOP should not be issued as we don't control the
  bus
- IP interrupt received - this is sent when transfer length is set to 0
  for auto/sequence command. The check for that is done before START is
  send so no STOP is required
- TSS received between commands - STOP is issued by the controller

Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>