rockchip: Add support to generate GZIP compressed U-boot binary

Add support for generating a GZIP-compressed U-boot binary with the
help of binman, if CONFIG_SPL_GZIP is selected.

Signed-off-by: Manoj Sai <abbaraju.manojsai@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>

arch/arm/dts/rockchip-u-boot.dtsi

@@ -56,10 +56,17 @@
 #else
 					arch = "arm";
 #endif
+#if defined(CONFIG_SPL_GZIP)
+					compression = "gzip";
+#else
 					compression = "none";
+#endif
 					load = <CONFIG_TEXT_BASE>;
 					entry = <CONFIG_TEXT_BASE>;
 					u-boot-nodtb {
+#if defined(CONFIG_SPL_GZIP)
+					compress = "gzip";
+#endif
 					};
 #ifdef CONFIG_SPL_FIT_SIGNATURE
 					hash {