apbuart: Depend upon sparc.

It absolutely needs to be able to get at pdev_archdata members
which are sparc specific.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>

drivers/tty/serial/Kconfig

@@ -1506,7 +1506,7 @@ config SERIAL_BCM63XX_CONSOLE
 
 config SERIAL_GRLIB_GAISLER_APBUART
 	tristate "GRLIB APBUART serial support"
-	depends on OF
+	depends on OF && SPARC
 	select SERIAL_CORE
 	---help---
 	Add support for the GRLIB APBUART serial port.