dmaengine: idxd: set max_xfer and max_batch for RO device

Load the max_xfer_size and max_batch_size values from the values read from
registers to the shadow variables. This will allow the read-only device to
display the correct values for the sysfs attributes.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/164971507673.2201761.11244446608988838897.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>