arm64: defconfig: Enable MFD_AXP20X_RSB

The Allwinner A64 SoC is paired with the X-Powers AXP803 PMIC over the
Reduced Serial Bus (RSB).

Enable the driver for this PMIC.
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
[wens@csie.org: Refined commit message]
Signed-off-by: Chen-Yu Tsai <wens@csie.org>

arch/arm64/configs/defconfig

@@ -312,6 +312,7 @@ CONFIG_MESON_GXBB_WATCHDOG=m
 CONFIG_MESON_WATCHDOG=m
 CONFIG_RENESAS_WDT=y
 CONFIG_BCM2835_WDT=y
+CONFIG_MFD_AXP20X_RSB=y
 CONFIG_MFD_CROS_EC=y
 CONFIG_MFD_CROS_EC_I2C=y
 CONFIG_MFD_CROS_EC_SPI=y