dmaengine: qcom_hidma: cleanup sysfs entries during remove

The 4.8-rc8 kernel is printing duplicate file entry warnings while removing
the HIDMA object. This is caused by stale sysfs entries remaining from the
previous execution.

_sysfs_warn_dup+0x5c/0x78
 sysfs_add_file_mode_ns+0x13c/0x1c0
 sysfs_create_file_ns+0x2c/0x40
 device_create_file+0x54/0xa0
 hidma_probe+0x7c8/0x808

Create hidma_sysfs_init and hidma_sysfs_uninit functions and call them from
the probe and remove path. To do proper clean up, adding the attrs object
to the device data structure to keep it around until remove call is made.

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>