MIPS: Loongson-3: Reserve 32MB for RS780E integrated GPU

MIPS: Loongson-3: Reserve 32MB for RS780E integrated GPU

Due to datasheet, reserving 0xff800000~0xffffffff (8MB below 4GB) is
not enough for RS780E integrated GPU's TOM (top of memory) registers
and MSI/MSI-x memory region, so we reserve 0xfe000000~0xffffffff (32MB
below 4GB).

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Steven J . Hill <sjhill@realitydiluted.com>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12889/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>