arch: Add support for 'notification reset' for aarch64 platforms

__fwk_notification_reset() call was done at the end of armv8-a boot code.
Add the support for aarch64 platforms (only if the build define
BUILD_HAS_NOTIFICATION flag, like it's done on armv8-a code)

Signed-off-by: Florian Sylvestre <fsylvestre@baylibre.com>