sfxge: Remove extra cache-line alignment and reorder sfxge_evq_t

[arybchik]

Summary

Remove the first member alignment to cacheline since it is nop.
Use __aligned() for the whole structure to make sure that the structure
size is cacheline aligned.
Remove lock alignment to make the structure smaller and fit all members
used on event queue processing into one cacheline (128 bytes) on x86-64.
The lock is obtained as well from different context when event queue
statistics are retrived from sysctl context, but it is infrequent.
Reorder members to avoid padding and go in usage order on event
processing.

[gnn]

Remember to put Approved by: gnn (mentor) in the commit message.

[arybchik]

Committed to head