Some old assemblers can't cope with r0 in address. It's actually
sensible thing to do, because r0 is shunted to 0 in address arithmetic
and by refusing r0 assembler effectively makes you understand that.

(Imported from upstream's a54aba531327285f64cf13a909bc129e9f9d5970.)

This also pulls in a trailing whitespace fix from upstream's
609b0852e4.

Change-Id: Ieec0bc8d24b98f86ce4fc9ee6ce5126d127cf452
Reviewed-on: https://boringssl-review.googlesource.com/12188
Reviewed-by: Adam Langley <agl@google.com>

This change adds AES and GHASH assembly from upstream, with the aim of
speeding up AES-GCM.

The PPC64LE assembly matches the interface of the ARMv8 assembly so I've
changed the prefix of both sets of asm functions to be the same
("aes_hw_").

Otherwise, the new assmebly files and Perlasm match exactly those from
upstream's c536b6be1a (from their master branch).

Before:
Did 1879000 AES-128-GCM (16 bytes) seal operations in 1000428us (1878196.1 ops/sec): 30.1 MB/s
Did 61000 AES-128-GCM (1350 bytes) seal operations in 1006660us (60596.4 ops/sec): 81.8 MB/s
Did 11000 AES-128-GCM (8192 bytes) seal operations in 1072649us (10255.0 ops/sec): 84.0 MB/s
Did 1665000 AES-256-GCM (16 bytes) seal operations in 1000591us (1664016.6 ops/sec): 26.6 MB/s
Did 52000 AES-256-GCM (1350 bytes) seal operations in 1006971us (51640.0 ops/sec): 69.7 MB/s
Did 8840 AES-256-GCM (8192 bytes) seal operations in 1013294us (8724.0 ops/sec): 71.5 MB/s

After:
Did 4994000 AES-128-GCM (16 bytes) seal operations in 1000017us (4993915.1 ops/sec): 79.9 MB/s
Did 1389000 AES-128-GCM (1350 bytes) seal operations in 1000073us (1388898.6 ops/sec): 1875.0 MB/s
Did 319000 AES-128-GCM (8192 bytes) seal operations in 1000101us (318967.8 ops/sec): 2613.0 MB/s
Did 4668000 AES-256-GCM (16 bytes) seal operations in 1000149us (4667304.6 ops/sec): 74.7 MB/s
Did 1202000 AES-256-GCM (1350 bytes) seal operations in 1000646us (1201224.0 ops/sec): 1621.7 MB/s
Did 269000 AES-256-GCM (8192 bytes) seal operations in 1002804us (268247.8 ops/sec): 2197.5 MB/s

Change-Id: Id848562bd4e1aa79a4683012501dfa5e6c08cfcc
Reviewed-on: https://boringssl-review.googlesource.com/11262
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>