uboot-rockchip: add Rock Pi E support

Add support for the Radxa Rock Pi E.

Signed-off-by: Tianling Shen <cnsztl@immortalwrt.org>
(cherry picked from commit 4459de8c79)

package/boot/uboot-rockchip/Makefile

@@ -75,6 +75,13 @@ define U-Boot/roc-cc-rk3328
     firefly_roc-rk3328-cc
 endef
 
+define U-Boot/rock-pi-e-rk3328
+  $(U-Boot/Default/rk3328)
+  NAME:=Rock Pi E
+  BUILD_DEVICES:= \
+    radxa_rock-pi-e
+endef
+
 # RK3399 boards
 
 define U-Boot/Default/rk3399
@@ -183,6 +190,7 @@ UBOOT_TARGETS := \
   orangepi-r1-plus-rk3328 \
   orangepi-r1-plus-lts-rk3328 \
   roc-cc-rk3328 \
+  rock-pi-e-rk3328 \
   fastrhino-r66s-rk3568 \
   fastrhino-r68s-rk3568 \
   mrkaio-m68s-rk3568 \