powerpc: Add PVN support for HeXin C2000 processor

HeXin Tech Co. has applied for a new PVN from the OpenPower Community
for its new processor C2000. The OpenPower has assigned a new PVN
and this newly assigned PVN is 0x0066, add pvr register related
support for this PVN.

Signed-off-by: Zhao Ke <ke.zhao@shingroup.cn>
Link: https://discuss.openpower.foundation/t/how-to-get-a-new-pvr-for-processors-follow-power-isa/477/10


Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231129075845.57976-1-ke.zhao@shingroup.cn