lscpu: add procfs–sysfs dump from Milk-V Pioneer

lscpu: add procfs–sysfs dump from Milk-V Pioneer

already in tree:

 rv64-linux: just a BeagleV Starlight SBC (no longer in production)
 rv64-visionfive2 is interesting because it's a system with an odd CPU count / mix of core types (4+1)

new dump:

 rv64-milkvpioneer is interesting because it's arguably a server board, i.e. with a whole bunch of cores and NUMA nodes.

[kzak@redhat.com: - add this commit message]

Signed-off-by: Jan Engelhardt <jengelh@inai.de>