This patch adds gpio driver supporting driver model for stm32f7 gpio.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Christophe KERELLO <christophe.kerello@st.com>
[trini: Add depends on STM32]
Signed-off-by: Tom Rini <trini@konsulko.com>