bhyve: improve acpi table generation

[corvink]

Summary

My qemu fwcfg patch (D31578) gets no review. So, it'll probably take much time to get merged. I did the work to split off the qemu fwcfg requirement from my acpi table generation rework. The acpi table generation without qemu fwcfg support looses some flexibility but it's still an improvement.

This patch improves the acpi table generation in two ways:

1. acpi tables are generated and loaded dynamically. No static offsets any more.
2. iasl isn't required any more for acpi table generation (not true for dsdt)

For easier review and committing, I'll create multiple patches for it. There's also a github branch which splits it into several commits (https://github.com/Beckhoff/freebsd-src/commits/phab/corvink/acpi-tables):

1. D36984
2. D36985
3. D36986
4. D36987
5. D36988
6. D36989
7. D36990
8. D36991
9. D36992
10. D36993
11. D36994
12. D36995
13. D36996
14. D36997
15. D36998
16. D36999
17. D37000
18. D37001
19. D37002

[corvink]

This revision was intended as overview about my patch series. Phabricator has a stack feature for this purpose so it's not required any more.

Thanks to jhb@ who showed me the stack feature.