spapr, spapr_nvdimm: fold NVDIMM validation in the same place

spapr, spapr_nvdimm: fold NVDIMM validation in the same place

NVDIMM has different contraints and conditions than the regular
DIMM and we'll need to add at least one more.

Instead of relying on 'if (nvdimm)' conditionals in the body of
spapr_memory_pre_plug(), use the existing spapr_nvdimm_validate_opts()
and put all NVDIMM handling code there. Rename it to
spapr_nvdimm_validate() to reflect that the function is now checking
more than the nvdimm device options. This makes spapr_memory_pre_plug()
a bit easier to follow, and we can tune in NVDIMM parameters
and validation in the same place.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20200825215749.213536-3-danielhb413@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>