arm64: Enable interrupts before calling do_notify_resume()

task_work_run() implementation had the side effect of enabling
interrupts. With commit ac3d0da8 (task_work: Make task_work_add()
lockless), interrupts are no longer enabled revealing the bug in the
arch code. This patch enables the interrupt explicitly before calling
do_notify_resume().

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>