stm32f4: Update GPIODirection usage
stm32f4: Fix uint casts
stm32f4: Fix abort usages
Merge pull request #88 from bgamari/stm32-fixes

STM32F4 fixes

Reviewed-by: farcaller
Enable zinc tests
Add tests to CharIO
Fix LCD pixel function argument types
This comparison is useless due to type limits
This should work, but needs a unit test
Added a dummy test to LCD driver
Need to make TestCharIO public
Add TestLCD stub 2-dimentional pixbuf
Add tests for drawing and fix b45f3fe