* alpha-tdep.c (alpha_next_pc): Use alpha_read_insn.

        (alpha_sigtramp_frame_this_id): Use get_frame_memory.
        (alpha_sigtramp_frame_prev_register): Likewise.
        (alpha_heuristic_frame_prev_register): Likewise.
        * alpha-mdebug-tdep.c (alpha_mdebug_frame_prev_register): Likewise.