x86/insn, tools/x86: Fix undefined behavior due to potential unaligned accesses

Don't perform unaligned loads in __get_next() and __peek_nbyte_next() as
these are forms of undefined behavior:

"A pointer to an object or incomplete type may be converted to a pointer
to a different object or incomplete type. If the resulting pointer
is not correctly aligned for the pointed-to type, the behavior is
undefined."

(from http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf

)

These problems were identified using the undefined behavior sanitizer
(ubsan) with the tools version of the code and perf test.

 [ bp: Massage commit message. ]

Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lkml.kernel.org/r/20210923161843.751834-1-irogers@google.com