lib: introduce some memory copy macros and functions
Changes from V1 to V2:
- change the version of GPL from version 2.1 to version 2

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@xxxxxxxxxxxxxx>