Bundle vcpu_time and vcpu_info structures together into a single

Bundle vcpu_time and vcpu_info structures together into a single
structure that is 64 bytes on x86. This ensures that indexing into
the array is fast (power-of-two size) and that accesses are cache
friendly (cache line size is usually 32 or 64 bytes).

Rename vcpu_data to vcpu_info, vcpu_time to vcpu_info.time.

Signed-off-by: Keir Fraser <keir@xensource.com>