serial: fix pch_uart kconfig & build

The dma_request_channel/dma_release_channel interfaces are not
built when DMADEVICES is not enabled, so make the driver depend on
DMADEVICES.  Also, the help text says that the driver enables & uses
PCH_DMA, which is not enabled, so select that.

ERROR: "__dma_request_channel" [drivers/serial/pch_uart.ko] undefined!
ERROR: "dma_release_channel" [drivers/serial/pch_uart.ko] undefined!

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Tomoya MORINAGA <tomoya-linux@dsn.okisemi.com>
Reported-by: Zimny Lech <napohybelskurwysynom2010@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/serial/Kconfig

@@ -1650,8 +1650,9 @@ config SERIAL_IFX6X60
 
 config SERIAL_PCH_UART
 	tristate "Intel EG20T PCH UART"
+	depends on PCI && DMADEVICES
 	select SERIAL_CORE
-	depends on PCI
+	select PCH_DMA
 	help
 	  This driver is for PCH(Platform controller Hub) UART of Intel EG20T
 	  which is an IOH(Input/Output Hub) for x86 embedded processor.