packagegroup-go-sdk-target: Enable on rv64

RISCV64 now supports golang (starting dunfell), therefore limit
disabling to rv32 only.

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