turnip: Use Mesa's libsync.h instead of libdrm's libsync.h.

Given that we already link to Android's libsync, use it instead of using a
build-time dependency on libdrm for the KGSL path.  This also would help
for older kernel compat with KGSL.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6821>
2 files changed