[POWERPC] Add support for R_PPC_ADDR16_HI relocations

apply_relocate_add() does not support R_PPC_ADDR16_HI relocations, which
prevents some non gcc-built modules to be loaded.

Signed-off-by: Simon Vallet <svallet@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>