MAINTAINERS: Add Loongson-2/Loongson-3 maintainers

Add Jiaxun Yang as the MIPS/Loongson-2 maintainer and add Huacai Chen
as the MIPS/Loongson-3 maintainer.

[ralf@linux-mips.org: Don't put all of drivers/platform/mips/ into these
two entries but rather only the files required even though at this time
the Loongson platforms are the only users of drivers/platform/mips/.]

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: James Hogan <james.hogan@mips.com>
Cc: Rui Wang <wangr@lemote.com>
Cc: Binbin Zhou <zhoubb@lemote.com>
Cc: Ce Sun <sunc@lemote.com>
Cc: Yao Wang <wangyao@lemote.com>
Cc: Liangliang Huang <huangll@lemote.com>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: r@hev.cc
Cc: zhoubb.aaron@gmail.com
Cc: huanglllzu@163.com
Cc: 513434146@qq.com
Cc: 1393699660@qq.com
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Patchwork: https://patchwork.linux-mips.org/patch/17888/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: James Hogan <jhogan@kernel.org>