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