ANDROID: add gki_module headers to .gitignore file

In commit f8bd6cf7 ("ANDROID: GKI: Add module load time protected
symbol lookup") the kernel/gki_module_exported.h and
kernel/gki_module_protected.h files are created, but these generated
files are not added to the .gitignore file, making them show up as added
files when building the tree.

Resolve this by adding them to the proper .gitignore file

Bug: 200082547
Fixes: f8bd6cf7 ("ANDROID: GKI: Add module load time protected symbol lookup")
Cc: Ramji Jiyani <ramjiyani@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I906ddd24bfc54d62f572fba5491e2d2025325957