rust: add powerpc-linux as a target platform

Changed files
+1
pkgs
development
compilers
rust
+1
pkgs/development/compilers/rust/binary.nix
···
"armv7l-linux"
"i686-linux"
"loongarch64-linux"
+
"powerpc-linux"
"powerpc64-linux"
"powerpc64le-linux"
"riscv64-linux"