On some architectures (powerpc in particular), the number of registers
exceeds what can be represented in an integer bitmask. Ensure we
generate the proper bitmask on such platforms.

Fixes: 71ad0f5e ("perf tools: Support for DWARF CFI unwinding on post processing")
Signed-off-by: NNaveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>