stm32f7: use stm32f7 gpio driver supporting driver model

With this gpio driver supporting DM, there is no need to enable clocks
for different gpios (for pin muxing) in the board specific code.

Need to increase the allocatable area required before relocation from 0x400 to
0xC00 becuase of 10 new gpio devices(& new gpio class) added in device tree.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
cc: Christophe KERELLO <christophe.kerello@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>