ARM: shmobile: koelsch: (1+1)GiB memory in DT

Fix dts to have memory 1GiB @ 0_4000_0000 + 1GiB @ 2_0000_0000
according to Koelsch's hardware manual.

Signed-off-by: Takashi Yoshii <takasi-y@ops.dti.ne.jp>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>