IMPORT: ebmb: optimize the lookup for modern CPUs

IMPORT: ebmb: optimize the lookup for modern CPUs

This is the same principles as for the latest improvements made on
integer trees. Applying the same recipes made the ebmb_lookup()
function jump from 10.07 to 12.25 million lookups per second on a
10k random values tree (+21.6%).

It's likely that the ebmb_lookup_longest() code could also benefit
from this, though this was neither explored nor tested.

This is ebtree commit a159731fd6b91648a2fef3b953feeb830438c924.