Simplify crypto IOV helpers

Expand the concept of an IOV block state into a cursor which remembers
the IOV set being iterated over, the block size, and both input and
output positions.  Eliminate the no-copy inline block getter for now,
but provide helpers to grab contiguous chains of blocks from a cursor.
Also provide an inline helper to sum the total length of an iov chain.
Refactor AES, Camellia builtin enc providers

In preparation for AES-NI support, adjust the block encryption helpers
in the AES enc provider so that the cache is only touched by helpers,
and reframe the CTS operations in terms of CBC operations.  Change the
Camellia enc provider as well for consistency.
Add Intel AESNI assembly files

Add assembly files from the Intel AESNI Sample Library, version 1.2,
which implement AES encryption using AES-NI instructions.  Trailing
whitespace was removed.
Adjust AESNI sources for krb5 tree

Remove functions we don't need.  Add macros to redefine functions with
an appropriate namespace prefix.
Add AES-NI support on Linux

If yasm and cpuid.h are present on a Linux i686 or x64 system, compile
the modified Intel AES-NI assembly sources.  In the builtin AES enc
provider, check at runtime whether the CPU supports AES-NI
instructions and use the assembly functions if so.