boards + cpu: atmega2560: fix non-existent GPIO
drivers/periph/gpio: fix #ifdef instead of #if
Merge pull request #1831 from LudwigOrtmann/periph_gpio_ifdef

drivers/periph/gpio: fix #ifdef instead of #if
lint: fix unassignedVariable warnings in stm32f1
lint: fix unusedVariable warnings
lint: fix redundantAssignment warnings
lint: fix unreadVariable warnings
lint: fix variableScope warnings
lint: fix invalidPrintfArgType_sint  warning
lint: fix uselessAssignmentPtrArg

    I've chosen to supress instead of removing the assignment because it looks
    like it may introduce a timing bias in the crypto code otherwise.
lint: fix warnings of possible nullPointer dereferences
lint: fix nullPointer errors
lint: fix syntaxError warning
cpu: stm32f1 spi: fix typos
lint: suppress warning about obsoleteFuntionsasctime