event/octeontx: fix build with clang 6

event/octeontx: fix build with clang 6

Clang 6 & 7 fail to naturally align packed structs due to this clang
can't use 8byte atomic primitives and splits them into lesser atomic
primitives. To use lesser atomic primitives we need to link libatomic
(-latomic), instead supply alignment attribute to the compiler.

timvf_worker.c:(.text+0x498): undefined reference to `__atomic_fetch_add_8'
timvf_worker.c:(.text+0x525): undefined reference to `__atomic_store_2'
timvf_worker.c:(.text+0x557): undefined reference to `__atomic_fetch_add_4'
timvf_worker.c:(.text+0x5de): undefined reference to `__atomic_store_2'

Fixes: f874c1eb1519 ("event/octeontx: create and free timer adapter")

Reported-by: Andrew Rybchenko <arybchenko@solarflare.com>
Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>