initrd: Not everyone keeps their source in /usr/src.
kernel/acpi: In the OS dependent layer, sync the debug code w/ FreeBSD.

* Remove an unused function.

* Enter the debugger only when ACPI_DEBUG is set.

* Fix indent and whitespace.
acpi: machdep.acpi_root should have the RSDP, so taking that should be fine.
loader/acpi: Fix/remove some comments and remove a misleading error msg.