MFC r341101-r341103, r341148, r341391, r341422-r341423, r341454, r341780-r341781, r341805, r342026

Make powerpc booke kernels boot from ubldr.

r341101: powerpcspe: Don't crash the loader on ubldr with SPE instructions.
r341102: powerpc: Prepare Book-E kernels for KERNBASE != run base
r341103: powerpc: Fix the powerpc64 build post-r341102
r341148: powerpc: Don't include KERNBASE in genassym, it's unnecessary
r341391: ubldr: Force 'usefdt' variable to 1 for powerpc
r341422: powerpc/booke: Check for the metadata address by physical address
r341423: powerpc: Check for a fdt in the metadata if it doesn't already exist
r341454: powerpc: preload_addr_relocate is no longer necessary for booke
r341780: powerpc/ubldr: Teach powerpc's ubldr to boot 64-bit kernels
r341781: powerpc/booke: Replace a logical equivalent of pmap_kextract() with a

real call

r341805: powerpc/booke: Don't get and use the load offset for TOC on APs
r342026: powerpc/booke: Change KERNBASE to be physical load address