Re-enable aarch64 neon instruction in vlib_buffer_free_inline

int vaddvq_u8 (uint8x16_t __a) is not appropriate to implement xxx_is_all_zero,
as there may be overflow causing incorrect return value.

Here's an example.
u8x16 x = {0 <repeats 12 times>, 1, 255, 0, 0};

Change-Id: Ia6a10bdf8da360dec12db902d028751a1a77e9a4
Signed-off-by: Lijian Zhang <Lijian.Zhang@arm.com>
Reviewed-by: Sirshak Das <Sirshak.Das@arm.com>