mali-t76x: depends on mesa3d-headers

mali-t76x: depends on mesa3d-headers

It selects them, but doesn't depend on them, and since the package only
provides binaries there's a complete lack of headers. When some other
package pulls in the egl/gles provider this doesn't result in headers
being pulled in, hence the API is completely missing. Fixes:
http://autobuild.buildroot.net/results/dab/dab91372b7bfde57796a7e3de7e823dc44adfb76/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>