Move macppc bootable installcd stuff to sys/arch/macppc/stand dirs.

- move installboot (for CD ISO) and mkboothfs (for mkhybrid(8)) tools to
sys/arch/macppc/stand
- also build mkboothfs as ${TOOL_

Move macppc bootable installcd stuff to sys/arch/macppc/stand dirs.

- move installboot (for CD ISO) and mkboothfs (for mkhybrid(8)) tools to
sys/arch/macppc/stand
- also build mkboothfs as ${TOOL_MACPPCMKBOOTHFS} in src/tools
- explicitly generate boothfs file (for mkhybrid(8)) in
sys/arch/macppc/stand/boothfs and install it into /usr/mdec
- use installed /usr/mdec/boothfs to create macppc bootable iso
- move list files for mkhybrid(8) hfs options to etc/etc.macppc

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