Remove spurious configuration of whole GPIOA bank

This is not an issue as long as SetupLED() is the first place
the GPIOA bank is configured so all the other ports are
floating inputs anyway, but it can kick in if the order
is changed.

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>
Avoid hardcoding of LED, Button and USB disconnect banks and pins

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>
Allow passing PLATFORM to the build to specify target board type

Example:
make PLATFORM=MAPLE

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>
Add MAPLE_MINI platform build option

Example:
make PLATFORM=MAPLE_MINI

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>