Current LSB 4.1 test suite still check libpng12.so, so add libpng 1.2.x
back, and set it as default verison for linuxstdbase image.
[YOCTO #4015]
(From OE-Core rev: f2463ce26706b971dad0116e8b92f9d55e945137)
Signed-off-by: Kang Kai <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>