x86: intel64: set page tables for every CPU

The page tables to use are now stored in the cpuboot struct.
For the first CPU, we set to the flat page tables, and then
update later in z_x86_prep_c() once the runtime tables have
been generated.

For other CPUs, by the time we get to z_arch_start_cpu()
the runtime tables are ready do go, and so we just install
them directly.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>