Instead of guessing at a sufficient size for the CPU VCRAT, base the
size on the number of online NUMA nodes.

v2: fix warning
Signed-off-by: Kent Russell <kent.russell@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>