Brltty support for dracut

This module provides brltty functionality in the initrd.
Module pickups user settings from system and install
necessary files like drivers and used text tables to initramfs.

For now the module is reliably functional from phase pre-mount
in earlier phases the module is not functional

TBD fix functionality from earlier phases than pre-mount

Module in instalation takes some options from environment variables.

BRLTTY_DRACUT_INCLUDE_DRIVERS forces include of screen or braille
driver
example:
BRLTTY_DRACUT_INCLUDE_DRIVERS=bpm beu

BRLTTY_DRACUT_INCLUDE_TEXT_FILES forces include of text tables
example:
BRLTTY_DRACUT_INCLUDE_TEXT_FILES=kok.ttb lv.tti

BRLTTY_LOCALE needs to be used when building initram image
to install used text table 
see https://bugzilla.redhat.com/show_bug.cgi?id=1584036
example
BRLTTY_LOCALE=cs_CZ.UTF-8

Module allows to override some settings from grub
mainly for debugging purposes

brltty.braille_parameters
example:
brltty.braille_parameters="auth=none,host=IP:0"

brltty.braille_driver
example:
brltty.braile_driver="ba"