add REVIEWERS and get_reviewer.pl script

add REVIEWERS and get_reviewer.pl script

Copied from linux kernel (where it is called MAINTAINERS and
get_maintainer.pl), with minimal changes to script (to recognize
mesa src tree rather than linux kernel src tree, and to avoid
accidentaly CC'ing Linus Torvalds on mesa patches), and slimmed
down MAINTAINER file syntax to recognize that we don't really have
subsystem "maintainers" in the same sense as the linux kernel (ie. no
different mailing lists and git trees per subsystem).

The main point is to automate slapping on the correct CC's for patches
via git's --cc-cmd feature, more than anything else.

I didn't attempt to fully populate the REVIEWERS file, by a long shot.
This is an opt-in system and anyone else can add their own entries.

To utilize:

  git send-email --cc-cmd ./scripts/get_reviewer.pl ...

or to configure it to be the default:

  git config sendemail.cccmd ./scripts/get_reviewer.pl

Signed-off-by: Rob Clark <robclark@freedesktop.org>