ARM: add ELF_FDPIC support

This includes the necessary code to recognise the FDPIC format on ARM
and the ptrace command definitions used by the common ptrace code.

Based on patches originally from Mickael Guene <mickael.guene@st.com>.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Mickael GUENE <mickael.guene@st.com>
Tested-by: Vincent Abriou <vincent.abriou@st.com>
Tested-by: Andras Szemzo <szemzo.andras@gmail.com>