(Imported from upstream's 7be6bc68c6baef87d4d730c2505a05810a5a1684.)

Change-Id: Ib0be641308d63679065d704553a5a979f058e81c
Reviewed-on: https://boringssl-review.googlesource.com/4492
Reviewed-by: Adam Langley <agl@google.com>

This addresses

- request for improvement for faster key setup in RT#3576;
- clearing registers and stack in RT#3554 (this is more of a gesture to
see if there will be some traction from compiler side);
- more commentary around input parameters handling and stack layout
(desired when RT#3553 was reviewed);
- minor size and single block performance optimization (was lying around);

(Imported from upstream's 23f6eec71d)

This one is best reviewed by verifying that
23f6eec71dbd472044db7dc854599f1de14a1f48^ in upstream has the exact same
versions of these files (we had no local diffs), so we can just copy them
wholesale.

bssl speed reports a wash on my Mac. If I keep running it, different ones win
each time.

Change-Id: I729bd39cf0b3a30cc24de839e1c734dcaef972b8
Reviewed-on: https://boringssl-review.googlesource.com/4491
Reviewed-by: Adam Langley <agl@google.com>

(Imported from upstream's 2d4d9623da)

Improve CBC decrypt and CTR by ~13/16%, which adds up to ~25/33%
improvement over "pre-Silvermont" version. [Add performance table to
aesni-x86.pl].

(Imported from upstream's b347341c75)

(Imported from upstream's 5572bc4e2f)

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)