ARM: dts: omap5-evm: Fix size of memory defined for EVM

Memory present for OMAP5-evm is 2GB. But in dts file
it is specified as 1GB. Correcting the same.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>