Documentation: Fixes a term's translation in Documentation/zh_CN/arm64/memory.txt

Fixes a term's translation in Documentation/zh_CN/arm64/memory.txt
The modification is based on Catalin Marinas <catalin.marinas@arm.com>'s
suggestion:
    "memory" in "ffffffc000000000 ffffffffffffffff 256GB memory"
    should  be treated as "kernel logical memory map",
    so the translation should be "内核逻辑内存映射".

Signed-off-by: Fu Wei <tekkamanninja@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>