docs/zh_CN: riscv: Update the translation of vm-layout.rst to 5.19-rc1

Synchronous translation from upstream commit 9d19f2b5
("Documentation: riscv: Add sv48 description to VM layout")

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/10cd6a241a0266d1d19ee5f0b2177d7d14d17ed2.1654685338.git.zhoubinbin@loongson.cn


Signed-off-by: Jonathan Corbet <corbet@lwn.net>