powerpc: Do not run IFUNC resolvers for LD_DEBUG=unused [BZ #24214]

This patch adds the missing bits for powerpc and fixes both
tst-ifunc-fault-lazy and tst-ifunc-fault-bindnow failures on
powerpc-linux-gnu.

Checked on powerpc-linux-gnu and powerpc-linux-gnu-power4.

Reviewed-by: Florian Weimer <fweimer@redhat.com>
Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>