ramips: fix the memory map on FireWRT

Avoid the use of memory marked as reserved

MT7621 support 512MB memory.
According to "MT7621_ProgrammingGuide_Preliminary_Platform.pdf"
0x0~0x1c000000        448MB
0x20000000~0x4000000  64MB
total 512MB

Signed-off-by: wengbj <fl.service@t-firefly.com>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 45892

target/linux/ramips/dts/FIREWRT.dts

@@ -8,7 +8,7 @@
 
 	memory@0 {
 		device_type = "memory";
-		reg = <0x0 0x10000000>, <0x30000000 0x10000000>;
+		reg = <0x0 0x1c000000>, <0x20000000 0x4000000>;
 	};
 
 	chosen {