rockchip: rename "Rock Pi 4" to "Rock Pi 4A"

Kernel has added the different variants of the Rock Pi 4 in commit
b5edb0467370 ("arm64: dts: rockchip: Mark rock-pi-4 as rock-pi-4a
dts"). The former Rock Pi 4 is now Rock Pi 4A.

For compatibility with kernel 5.4, this rename has been held back
so far. Having switched to kernel 5.10 now, we can finally apply
it in our tree as well.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

package/boot/uboot-rockchip/Makefile

@@ -52,7 +52,7 @@ define U-Boot/rock-pi-4-rk3399
   BUILD_SUBTARGET:=armv8
   NAME:=Rock Pi 4
   BUILD_DEVICES:= \
-    radxa_rock-pi-4
+    radxa_rock-pi-4a
   DEPENDS:=+PACKAGE_u-boot-rock-pi-4-rk3399:arm-trusted-firmware-rockchip
   PKG_BUILD_DEPENDS:=arm-trusted-firmware-rockchip
   ATF:=rk3399_bl31.elf