MIPS: Loongson64: Disable exec hazard

Loongson64 has hardware mechanism to prevent hazard issue,
so we can simply disable exec hazard in cpu-features.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: chenhc@lemote.com
Cc: paul.burton@mips.com
Cc: linux-kernel@vger.kernel.org