[PATCH] Add preprocessed files (*.i) to .gitignore

The kernel build system supports making preprocessed files (*.i) from C source
files.  Add these files to .gitignore.

Signed-off-by: Josh Triplett <josh@freedesktop.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>