package/brltty: disable features and add optional dependencies

package/brltty: disable features and add optional dependencies

* --without-midi-package should fix a number of autobuild failures.
* Disable a number of speech drivers to avoid build failures
  if they are installed on the host.
* Optional dependency on espeak and flite fixes builds where
  espeak or flite are installed on the host.

Fixes:

  http://autobuild.buildroot.net/results/0c4f557c2ad276b1ed065119532af37c0af5f014
  http://autobuild.buildroot.net/results/ea82b7c7732821368746ddddb5d529e97c9b6c16

Signed-off-by: Mario Lang <mlang@blind.guru>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>