Move sync.h from staging into include/linux

The kgsl driver needs this to compile (or we could use .. but
this is easier).

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Cherry-picked from a0ab343c58f2412011ff2d544d2ef59a016f934c
[joshc: Handled sw_sync uapi split, move uapi component out of
drivers/staging]
Signed-off-by: Josh Cartwright <joshc@codeaurora.org>