MFC r329190, r329315, r330131: metadata load file unification
r329190: Unify metadata load files for arm, mips, powerpc, sparc64
Summary:
All metadata.c files are very similar, with only trivial changes. Unify them
into a single common file, with minor special-casing where needed.
r329315: stand: Fix ubldr after r329190
metadata load files were consolidated in r329190, and these relocation fixup
bits were inadvertently dropped in the process. Re-add them to fix boot with
ubldr.
r330131: Fix module loading on arm after the metadata.c unification in
r329190. Arm modules need an additional address fixup not needed by other
platforms.