dmaengine: idxd: Make read buffer sysfs attributes invisible for Intel IAA

dmaengine: idxd: Make read buffer sysfs attributes invisible for Intel IAA

In current code, the following sysfs attributes are exposed to user to
show or update the values:
  max_read_buffers (max_tokens)
  read_buffer_limit (token_limit)
  group/read_buffers_allowed (group/tokens_allowed)
  group/read_buffers_reserved (group/tokens_reserved)
  group/use_read_buffer_limit (group/use_token_limit)

>From Intel IAA spec [1], Intel IAA does not support Read Buffer
allocation control. So these sysfs attributes should not be supported on
IAA device.

Fix this issue by making these sysfs attributes invisible through
is_visible() filter when the device is IAA.

Add description in the ABI documentation to mention that these
attributes are not visible when the device does not support Read Buffer
allocation control.

[1]: https://cdrdv2.intel.com/v1/dl/getContent/721858

Fixes: fde212e44f45 ("dmaengine: idxd: deprecate token sysfs attributes for read buffers")
Fixes: c52ca478233c ("dmaengine: idxd: add configuration component of driver")
Signed-off-by: Xiaochen Shen <xiaochen.shen@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20221022074949.11719-1-xiaochen.shen@intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>