directfb: update to 1.4.15

directfb: update to 1.4.15

The newest version for directfb is 1.5.3 but it's instruction set base on armv6.
The current qemuarm don't have some instructions for armv6 because some codes of \
the new version of directfb more than 1.5 are realized with assemble language,for example the lock. \
I update this recipe to 1.4.15 for directfb running more platform.

Signed-off-by: Xiaofeng Yan <xiaofeng.yan@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>