ARM: shmobile: defconfig: Enable DMA for serial ports

DMA for (H)SCIF(A|B) serial ports on R-Car Gen2 and RZ/G1 SoCs is
considered stable, hence enable it by default.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/configs/shmobile_defconfig

@@ -107,6 +107,7 @@ CONFIG_SERIAL_8250_EM=y
 CONFIG_SERIAL_SH_SCI=y
 CONFIG_SERIAL_SH_SCI_NR_UARTS=20
 CONFIG_SERIAL_SH_SCI_CONSOLE=y
+CONFIG_SERIAL_SH_SCI_DMA=y
 CONFIG_I2C_CHARDEV=y
 CONFIG_I2C_MUX=y
 CONFIG_I2C_DEMUX_PINCTRL=y