nfit: make DIMM DSMs optional

Commit 4995734e973a "acpi, nfit: fix acpi_check_dsm() vs zero functions
implemented" attempted to fix a QEMU regression by supporting its usage
of a zero-mask as a valid response to a DSM-family probe request.
However, this behavior breaks HP platforms that return a zero-mask by
default causing the probe to misidentify the DSM-family.

Instead, the QEMU regression can be fixed by simply not requiring the DSM
family to be identified.

This effectively reverts commit 4995734e973a, and removes the DSM
requirement from the init path.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Cc: Linda Knippers <linda.knippers@hpe.com>
Fixes: 4995734e973a ("acpi, nfit: fix acpi_check_dsm() vs zero functions implemented")
Reported-by: Jerry Hoemann <jerry.hoemann@hpe.com>
Tested-by: Jerry Hoemann <jerry.hoemann@hpe.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>