lib: memcopy & string use glibc version [Miao Xie]

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.

Signed-off-by: Miao Xie <miaox*******>
Signed-off-by: faux123 <reioux@gmail.com>