Remove spurious configuration of whole lower GPIOA bank

This is not much of an issue as long as SetupLED() is the first place
the GPIOA bank is configured and the ports are inputs anyway, but it
would cause trouble if something tried to configure any of the ports
before SetupLED().

Note that ports are by default floating inputs after reset,
but this configuration was setting them to analog inputs instead.

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>