Revert "ANDROID: GKI: remove CONFIG_CMDLINE_EXTEND from arm64 gki_defconfig"

This reverts commit 4c2fb69c.

Bring back CONFIG_CMDLINE_EXTEND while we wait for an alternative
solution to be accepted upstream.

Bug: 120440972
[cmllamas: fix trivial revert conflict]
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Change-Id: I5d917d07d517ea07f5936a04b5f2b505af7c2b2d