dmaengine: IOATDMA: Cleanup pre v3.0 chansts register reads

Remove pre-3.0 channel status reads. 3.0 and later chansts register
is 64bit and can be read 64bit. This was clarified with the hardware
architects and since the driver now only support 3.0+ we don't need the
legacy support

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>