src/meta-openembedded:directfb: Add zlib PACKAGECONFIG

zlib was always enabled in DEPENDS and EXTRA_OEMAKE. Now it is
a PACKAGECONFIG which is enabled by default.

Signed-off-by: Ricardo Simoes <ricardo.simoespt.bosch.com>
Signed-off-by: Mark Jonas <mark.jonasde.bosch.com>
Signed-off-by: Khem Raj <raj.khemgmail.com>