binutils: Install PIC version of libiberty.a

some architectures e.g. mips complain in linking apps which have shared
libs that are linking with libiberty.a fixes errors like below

libiberty/../../libiberty/hashtab.c:285:(.text+0xf8): relocation R_MIPS_26 against `htab_create_typed_alloc' cannot be used when making a shared object; recompile with -fPIC

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>