Implement MK_NVME now that the expression for where NVMe is
complicated. Default it to "yes" for x86 and powerpc64 and
no everywhere else. Use it in camcontrol to define WITH_NVME
for those platforms where we support nvme.
This should fix the newly introduced nvme files to camcontrol
which were building everywhere.
Pointy Hat To: imp
Sponsored by: Netflix
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