ANDROID: GKI: Only protect exports if KMI symbols are present

Only enforce export protection if there are symbols in the
unprotected list for the Kernel Module Interface (KMI).

This is only relevant for targets like arm64 that have
defined ABI symbol lists. This allows non-GKI targets
like arm and x86 to continue using GKI source code
without disabling the feature for those targets.

Bug: 232430739
Test: TH
Fixes: fd1e7688 ("ANDROID: GKI: Protect exports of protected GKI modules")
Change-Id: Ie89e8f63eda99d9b7aacd1bb76d036b3ff4ba37c
Signed-off-by: Ramji Jiyani <ramjiyani@google.com>
(cherry picked from commit a6eaf3db)