gas: dw2gencfi: ignore all .cfi_* directives with --scfi=all

As we add support for --scfi=inline, this commit will need to evolve and
more changes may be necessary.  More specifically, we will need to
explictly check the value of the enumerator flag_synth_cfi.

gas/
        * dw2gencfi.c (dot_cfi): Ignore processing when synthesizing
	CFI.
        (dot_cfi_escape): Likewise.
        (dot_cfi_personality): Likewise.
        (dot_cfi_lsda): Likewise.
        (dot_cfi_val_encoded_addr): Likewise.
        (dot_cfi_label): Likewise.
        (dot_cfi_sections): Likewise.
        (dot_cfi_startproc): Likewise.
        (dot_cfi_endproc): Likewise.
        (dot_cfi_personality_id): Likewise.
        (dot_cfi_fde_data): Likewise.
        (dot_cfi_inline_lsda): Likewise.