serial: atmel: allow compile testing on non-atmel architectures

This commit also fixes compiler warnings and errors seen when building
on x86_64.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -115,9 +115,9 @@ config SERIAL_SB1250_DUART_CONSOLE
 
 config SERIAL_ATMEL
 	bool "AT91 / AT32 on-chip serial port support"
-	depends on ARCH_AT91 || AVR32
+	depends on ARCH_AT91 || AVR32 || COMPILE_TEST
 	select SERIAL_CORE
-	select SERIAL_MCTRL_GPIO
+	select SERIAL_MCTRL_GPIO if GPIOLIB
 	help
 	  This enables the driver for the on-chip UARTs of the Atmel
 	  AT91 and AT32 processors.