EDK II: Add .gitignore

EDK II: Add .gitignore

While edk2 is still maintained in SVN, Many edk2 developers use git
for their main workflow, using the official mirrors.

Add a .gitignore to the EDK II root, BaseTools and Conf directories to
prevents files generated as part of the build from cluttering up "git
status" output.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>
[removed Linaro-specific bits, rework for upstream]
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16213 6f19259b-4bc3-4df7-8a09-765794883524