util: add bash completion script

Add a bash script for the flashrom CLI that auto-completes the command
sequence. The script is generated from a template by substituting a
list of enabled programmers. It requires an extra `bash-completion`
package to work, but, fortunately, it's installed on most systems.

Also, provide the meson option `bash_completion` to determine if the
script should be installed.

Change-Id: Ie68bc91c3cea4de2ffdbeffd07e48edd8d5590e1
Signed-off-by: Alexander Goncharov <chat@joursoir.net>
---
M .gitignore
M Makefile
M meson.build
M meson_options.txt
A util/flashrom.bash-completion.tmpl
5 files changed, 179 insertions(+), 2 deletions(-)