dmaengine: idxd: check GENCAP config support for gencfg register

dmaengine: idxd: check GENCAP config support for gencfg register

[ Upstream commit 79c4c3db7d86b9bec94562275efc82e58f3d0132 ]

DSA spec 1.2 has moved the GENCFG register under the GENCAP configuration
support with respect to writability. Add check in driver before writing to
GENCFG register.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/163406171896.1303830.11217958011385656998.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>