acpi: switch to dynamic mapping at SYS_STATE_boot

acpi: switch to dynamic mapping at SYS_STATE_boot

We can switch ACPI from using fixmap to dynamic mapping as soon as
the system enters SYS_STATE_boot. This will allow us, for example,
to map MADT on systems with large number of processors where the
table might not fit into NUM_FIXMAP_ACPI_PAGES (currently set to 4).

To avoid having a window between system entering SYS_STATE_boot and
vmap area being initialized move vm_init() a little higher.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>