bhyve: Let BASL compile with raised warnings

• Make basl_dump() as unused.
• Avoid arithmetic on a void pointer.
• Avoid a signed/unsigned comparison with BASL_TABLE_CHECKSUM_LEN_FULL_TABLE.
• Ignore warnings about unused parameters from stuff pulled in by acpi.h. In particular, any prototype wrapped by ACPI_DBG_DEPENDENT_RETURN_VOID() will raise such parameters unless ACPI_DEBUG_OUTPUT is defined.

Reviewed by: corvink, jhb
Differential Revision: https://reviews.freebsd.org/D37397