bhyve: make basl_table_add_* functions public

[corvink]

Summary

The code will be more readable if we use struct definition from ACPI-CA
to build ACPI tables. We can fill out the struct and append it to the
basl_table by using basl_table_append_bytes. After that, we have to
declare which checksums, length and pointers should be patched by basl.
That's done by the add_* functions.