gpio: stm32: Use macro to simplify registration

The registration of each GPIO bank differs by only few details. These
differences can be factorized in order to create a generic registration
macro.

This has several advantages:
- Less code
- Easier to add new banks
- Less work to add support for new STM32 families

The diff stat speaks for it-self: 26 insertions(+), 92 deletions(-)

Change-Id: I674752fda5ee3caefb815ccf070a1b636b16cf85
Signed-off-by: Florian Vaussard <florian.vaussard@heig-vd.ch>