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>
Git-commit: a0f3f0f28e1636405b4c736eb7b9bd557cf11ad7
Git-repo: https://android.googlesource.com/kernel/common.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>