acpi, nfit: rework NVDIMM leaf method detection

acpi, nfit: rework NVDIMM leaf method detection

BugLink: http://bugs.launchpad.net/bugs/1773233
commit 466d1493ea830789a2f063f478aaed2e324f0d3d upstream.

Some BIOSen do not handle 0-byte transfer lengths for the _LSR and _LSW
(label storage read/write) methods. This causes Linux to fallback to the
deprecated _DSM path, or otherwise disable label support.

Introduce acpi_nvdimm_has_method() to detect whether a method is
available rather than calling the method, require _LSI and _LSR to be
paired, and require read support before enabling write support.

Cc: <stable@vger.kernel.org>
Fixes: 4b27db7e26cd ("acpi, nfit: add support for the _LS...")
Suggested-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>