libnvdimm, dimm: Maximize label transfer size

Use kvzalloc() to bypass the arbitrary PAGE_SIZE limit of label transfer
operations. Given the expense of calling into firmware, maximize the
amount of label data we transfer per call to be up to the total label
space if allowed by the firmware.

Instead of limiting based on PAGE_SIZE we can instead simply limit the
maximum size based on either the config_size int he case of the get
operation, or the length of the write based on the set operation.

On a system with 24 NVDIMM modules each with a config_size of 128K and a
maximum transfer size of 64K - 4, this patch reduces the init time for the
label data from around 24 seconds down to between 4-5 seconds.

Reviewed-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>