arch/x86: (Intel64) use per-CPU parameter struct for CPU startup

A new 'struct x86_cpuboot' is created as well as an instance called
'x86_cpuboot[]' which contains per-CPU boot data (initial stack,
entry function/arg, selectors, etc.). The locore now consults this
table to set up per-CPU registers, etc. during early boot.

Also, rename tss.c to cpu.c as its scope is growing.

Signed-off-by: Charles E. Youse <charles.youse@intel.com>