[dev.power64] cmd/objdump: disable tests on power64/power64le
[dev.power64] cmd/objdump: disable tests on power64/power64le

LGTM=rsc, austin
R=austin, rsc, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/164300043

d0f/go-zh,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,d0f/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,d0f/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,d0f/go-zh,bryanxu/go-zh,webfd/go-zh