libgpg-error: Support build for native on ppc64/ppc64le hosts

libgpg-error: Support build for native on ppc64/ppc64le hosts

Both RHEL and SLES uses ppc64/ppc64le for powerpc 64 bit big/little
endian targets instead of powerpc64/powerpc64le in libgpg-error.

Also libgpg-error provides common target system names in form like
<arch>-unknown-linux-gnu.

Add mapping for ppc64/ppc64le targets to their libgpg-error equivalents
to fix native builds.

Cross build for arm64 tested on IBM Power 8 machine with RHEL7 for
ppc64le variant only, but should work for ppc64 as well.

(From OE-Core rev: f1af780769477f06eb925fd87c844baba04ada2d)

Signed-off-by: Serhey Popovych <serhe.popovych@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>