mediatek: add missing symbols for mt7622

Signed-off-by: John Crispin <[email protected]>

target/linux/mediatek/mt7622/config-4.14

@@ -418,7 +418,7 @@ CONFIG_SPI=y
 CONFIG_SPI_MASTER=y
 CONFIG_SPI_MT65XX=y
 CONFIG_SRCU=y
-# CONFIG_SWAP is not set
+CONFIG_SWAP=y
 CONFIG_SWIOTLB=y
 CONFIG_SWPHY=y
 CONFIG_SYSCTL_EXCEPTION_TRACE=y