MIPS: Loongson64: Select mac2008 only feature

Some Loongson-64 processor didn't set MAC2008 bit in fcsr,
but actually all Loongson64 processors are MAC2008 only.

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