sunxi: build kernel with sun6i-rtc driver

sun6i-rtc cannot be built as a module and the hardware is only
present in some of the sunxi SoCs, see driver source:
        { .compatible = "allwinner,sun6i-a31-rtc" },
        { .compatible = "allwinner,sun8i-a23-rtc" },
        { .compatible = "allwinner,sun8i-h3-rtc" },
        { .compatible = "allwinner,sun8i-r40-rtc" },
        { .compatible = "allwinner,sun8i-v3-rtc" },
        { .compatible = "allwinner,sun50i-h5-rtc" },
        { .compatible = "allwinner,sun50i-h6-rtc" },

Set CONFIG_RTC_DRV_SUN6I=y in kernel config file for cortexa7 and
cortexa53 subtargets which covers all of the above.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/sunxi/cortexa53/config-5.10

@@ -55,6 +55,7 @@ CONFIG_PINCTRL_SUN50I_H6_R=y
 CONFIG_QUEUED_RWLOCKS=y
 CONFIG_QUEUED_SPINLOCKS=y
 CONFIG_RODATA_FULL_DEFAULT_ENABLED=y
+CONFIG_RTC_DRV_SUN6I=y
 # CONFIG_SND_SUN50I_CODEC_ANALOG is not set
 CONFIG_SOUND_OSS_CORE_PRECLAIM=y
 CONFIG_SPARSEMEM=y

target/linux/sunxi/cortexa7/config-5.10

@@ -18,6 +18,7 @@ CONFIG_NET_DSA_TAG_BRCM_LEGACY=y
 CONFIG_NET_DSA_TAG_BRCM_PREPEND=y
 CONFIG_NET_SWITCHDEV=y
 CONFIG_NOP_USB_XCEIV=y
+CONFIG_RTC_DRV_SUN6I=y
 CONFIG_USB_MUSB_DUAL_ROLE=y
 # CONFIG_USB_MUSB_GADGET is not set
 CONFIG_USB_MUSB_HDRC=y