Subzero: Make InstX8632Cbwdq a UnaryOp.

After the changes in CL 443203003, InstX8632Cbwdq fits the template for
a UnaryOp, so change it to be in instance of this class.

BUG=none
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/452143003