ANDROID: fiq_debugger: add ARM64 support

Add fiq_debugger_arm64.c that implements the platform-specific
functions.

Change-Id: I4d8b96777bb8503a93d4eb47bbde8e018740a5bf
Signed-off-by: Colin Cross <ccross@android.com>

[AmitP: Remove unused stackframe -> sp to align with upstream commit
        31e43ad3 ("arm64: unwind: remove sp from struct stackframe")

        Also folded following android-4.9 commit changes into this patch
        a33d9f9fa333 ("ANDROID: fiq_debugger: Pass task parameter to unwind_frame()")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>