of: make drivers depend on CONFIG_OF instead of CONFIG_PPC_OF

Some OF drivers could likely be used on non-powerpc OF based platforms,
so fix the kconfig depends to be CONFIG_OF instead of CONFIG_PPC_OF.

Compile tested on ARM and sparc.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index aff9dcd..9d109f9 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -1402,7 +1402,7 @@
 
 config SERIAL_OF_PLATFORM
 	tristate "Serial port on Open Firmware platform bus"
-	depends on PPC_OF || MICROBLAZE
+	depends on OF
 	depends on SERIAL_8250 || SERIAL_OF_PLATFORM_NWPSERIAL
 	help
 	  If you have a PowerPC based system that has serial ports