gitignore: Ignore Eclipse (Xtensa Xplorer) project files.

When debugging Xtensa port, on needs for sure to create an Xtensa Xplorer
project in order to be able to debug his project. These files will appear
in the git repository as non versioned files. It is safe to ignore them as
we won't anybody commit these files (user specific).

Change-Id: I156ec5c7393f1db98286da0b841a4e8496a9ff89
Signed-off-by: Mazen NEIFER <mazen@nestwave.com>