async_tx: build-time toggling of async_{syndrome,xor}_val dma support

ioat3.2 does not support asynchronous error notifications which makes
the driver experience latencies when non-zero pq validate results are
expected.  Provide a mechanism for turning off async_xor_val and
async_syndrome_val via Kconfig.  This approach is generally useful for
any driver that specifies ASYNC_TX_DISABLE_CHANNEL_SWITCH and would like
to force the async_tx api to fall back to the synchronous path for
certain operations.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/crypto/async_tx/Kconfig b/crypto/async_tx/Kconfig
index e5aeb2b..e28e276 100644
--- a/crypto/async_tx/Kconfig
+++ b/crypto/async_tx/Kconfig
@@ -23,3 +23,8 @@
 	select ASYNC_CORE
 	select ASYNC_PQ
 
+config ASYNC_TX_DISABLE_PQ_VAL_DMA
+	bool
+
+config ASYNC_TX_DISABLE_XOR_VAL_DMA
+	bool