pinmux: stm32f4: Clean-up pinmux header

Clean-up the pinmux header as a preparatory work before adding more
pinmuxes.

This is achieved by the following two actions:
- Reorder the defines by increasing GPIO order to make it
  easier to add more pinmux over time while avoiding a huge mess
- Use tabs to align

Change-Id: I07d9ae28f61287748d33dcf638dcbf2e6865517b
Signed-off-by: Florian Vaussard <florian.vaussard@heig-vd.ch>