autoconf: only check for dev86 and iasl checks on x86

autoconf: only check for dev86 and iasl checks on x86

The previous patch (25331:dfe39bd65137) only touched the definition of the
variables used to refer to the paths to the tools but didn't remove the actual
checks.

Run autogen after applying this patch.

Signed-off-by: Roger Pau Monne <roger.pau@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
[ ijc -- added a comment about "build" vs "host" terminology and a note about
         the previous attempt to the changelog, reintroduce AC_CANONICAL_HOST
         which was remove by 25303:078c7d4cde1d after this patch was posted but
         is required for $host_cpu ]
Committed-by: Ian Campbell <ian.campbell@citrix.com>