board: synquacer: set actual gd->ram_top and gd->ram_size

Current gd->ram_size and gd->ram_top reflect only the
first DRAM bank even if the SynQuacer Developerbox could
have up to three DRAM banks.
With the commit 06d514d7 ("lmb: consider EFI memory map"),
the first DRAM bank indicates <4GB address, so whole >4GB memory
is marked as EFI_BOOT_SERVICES_DATA and it results that
U-Boot can not access >4GB memory.

Since 64-bits DRAM address is fully available on the SynQuacer
Developerbox, let's set the installed DIMM information to
gd->ram_top and gd->ram_size.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Acked-by: Jassi Brar <jaswinder.singh@linaro.org>