[ARM] arm64: Revert update in arch_delay_loop_cycles()

The commit 80bcb96b3ebc85e3d5ee4f493047459e53fd3ee6 "[ARM] arm64:
update arch_delay_loop_cycles()" tried to fix arch_delay_loop_cycles()
for Foundation-v8 model and Real HW but after trying number of times
on real HW it seems original way of calculatin machines cycles from
delay loop count works perfectly fine on real HW hence this patch.

Sorry for the unnecessary noise.

Signed-off-by: Anup Patel <anup@brainfault.org>