ANDROID: kbuild: disable GCOV with CFI

With GCOV enabled, LLVM generates calls to compiler-generated
__llvm_gcov_* functions, but doesn't add them to the CFI jump
table, which trips indirect call checking. Work around the issue
by disabling CFI when GCOV_KERNEL is enabled.

Bug: 169124292
Change-Id: Ifd60cd9eda2bcdd86838ac5ce41bb0dbc00d602f
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
(cherry picked from commit 93a4197bc23a4a6967ff0592d07f3cf4cd69b1d6)