ASL compiler will be used to build ACPI tables at runtime

We'll switch between precompiled AMLs (used now) and runtime-compiling
ACPI when starting xhyve. 'acpi.c' and 'acpitbl.c' have same acpi
tables offsets definitions. To prevent problems in future and partly
save compatibility with bhyve sources, rename definitios in 'acpitbl.c'

Since this moment we're assuming that ACPI tables build method will be
chosen at runtime.

If ASL compiler path specified - building ACPI tables using it, if not
- building them from existing AMLs

Wrapping functions with callbacks let us choose at runtime how the
tables should be built: using precompiled AMLs or using ASL compiler.

ASL-compiling method is gonna be updated, it doesn't work properly now

The bhyve acpi MADT table was given a static space of 256 (0x100) bytes,
this is enough space to allow VM_MAXCPU to be 21, this patch changes
that so VM_MAXCPU can be of arbitrary value and not overflow the space
by actually calculating the space needed for the table.

Based on freebsd/freebsd-src@5822161