powerpc/powernv: allocate sparse PE# when using M64 BAR in Single PE mode
When M64 BAR is set to Single PE mode, the PE# assigned to VF could be
sparse.
This patch restructures the code to allocate sparse PE# for VFs when M64
BAR is set to Single PE mode. Also it rename the offset to pe_num_map to
reflect the content is the PE number.
Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com> Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com> Acked-by: Alexey Kardashevskiy <aik@ozlabs.ru> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>