Just have the MD code provide syscall and have generic code for the
rest.
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D33515
Split the powerpc specific parts into kboot/arch/powerpc64. More may be
needed here.
Sponsored by: Netflix
Reviewed by: jhibbits
Differential Revision: https://reviews.freebsd.org/D33514