package/brltty: explicitly check if ioperm is available

package/brltty: explicitly check if ioperm is available

ioperm, inb and outb are i386 specific functions usually
not available on non-PC archs.  Check if ioperm is available before
trying to use it.

Patch cherry-picked from upstream, can be removed when 5.6 is out.

Fixes:
  http://autobuild.buildroot.net/results/f09974f2ba24319e55e578ece34bb2e7e8bb3c43
  http://autobuild.buildroot.net/results/7d502f280c46f0d1e2678140f9117fcc59bc2d7b

Signed-off-by: Mario Lang <mlang@blind.guru>
[Thomas: move patch out of per-version directory, add comment
explaining why we need to autoreconf, and why we can't use
<pkg>_AUTORECONF.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>