ANDROID: kleaf: make a note to sync define_common_kernels() and KMI_SYMBOL_LIST(S).

Right now, define_common_kernels() uses a logic
    kmi_symbol_lists = glob(["android/abi_gki_aarch64*"])
as the list of KMI symbols for aarch64 non debug builds.
If the list differs from
KMI_SYMBOL_LIST and ADDITIONAL_KMI_SYMBOL_LISTS,
the value needs to be manually overridden.

In addition, define_common_kernels() sets
    trim_nonlisted_kmi = not kmi_symbol_lists.empty()
for aarch64 non debug builds. If this value differs from
TRIM_NONLISTED_KMI, the value needs to be manually overriden.

To ensure that they don't get out of sync, add a note
in both places to keep them in sync.

In the future, we can load values from build.config like we
did for CLANG_VERSION in build.config.common. Then, this note
can be deleted.

Bug: 215745244
Test: none

Change-Id: I7e2c62e7dd97c6b06f4d628c3c8672922e99aaee
Signed-off-by: Yifan Hong <elsk@google.com>