ppc4xx: Move common dependency on serial to common option

All machines that select SERIAL also select PPC4XX so we can just add
this common dependency there once.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-Id: <94f1eb7cfb7f315bd883d825f3ce7e0cfc2f2b69.1609636173.git.balaton@eik.bme.hu>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/ppc/Kconfig

@@ -36,7 +36,6 @@ config PPC405
     select M48T59
     select PFLASH_CFI02
     select PPC4XX
-    select SERIAL
 
 config PPC440
     bool
@@ -45,7 +44,6 @@ config PPC440
     imply E1000_PCI
     select PCI_EXPRESS
     select PPC4XX
-    select SERIAL
     select FDT_PPC
 
 config PPC4XX
@@ -53,6 +51,7 @@ config PPC4XX
     select BITBANG_I2C
     select PCI
     select PPC_UIC
+    select SERIAL
 
 config SAM460EX
     bool
@@ -61,7 +60,6 @@ config SAM460EX
     select IDE_SII3112
     select M41T80
     select PPC440
-    select SERIAL
     select SM501
     select SMBUS_EEPROM
     select USB_EHCI_SYSBUS
@@ -123,7 +121,6 @@ config VIRTEX
     bool
     select PPC4XX
     select PFLASH_CFI01
-    select SERIAL
     select XILINX
     select XILINX_ETHLITE
     select FDT_PPC