Revert "ANDROID: GKI: Make linux_banner a C pointer"

This reverts commit fdef3b72. This
breaks ramdump parsing.

Bug: 154586724
Test: compile
Change-Id: Ia91f3e0d0a0cc67947081a73bdc61670f3a25185
Signed-off-by: Will McVicker <willmcvicker@google.com>