lib/memcopy: use glibc version

    the kernel's memcpy and memmove is very inefficient. But the glibc version is
    quite fast, in some cases it is 10 times faster than the kernel version. So I
    introduce some memory copy macros and functions of the glibc to improve the
    kernel version's performance.

    The strategy of the memory functions is:
    1. Copy bytes until the destination pointer is aligned.
    2. Copy words in unrolled loops.  If the source and destination are not
       aligned in the same way, use word memory operations, but shift and merge
       two read words before writing.
    3. Copy the few remaining bytes.
    lib/string: use glibc version

    the performance of memcpy and memmove of the general version is very
    inefficient, this patch improved them.