Time the Fibonacci function in iterations of 8^N, where N=[0..8]

Bug: b/148660286
Change-Id: Ief391a7f6181c5907de128f5c983ac32aeadfae0
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40949Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>