arm: mach-k3: Set NR_DRAM_BANKS to 2

arm: mach-k3: Set NR_DRAM_BANKS to 2

Set CONFIG_NR_DRAM_BANKS to 2 as we have two banks described in the
memory/ node for lower and higher addressible DDR regions.

This allows use of FDT functions from fdt_support.c to set up and fix up
the memory/ node correctly.

Signed-off-by: Neha Malcom Francis <n-francis@ti.com>
Signed-off-by: Santhosh Kumar K <s-k6@ti.com>