configs: am62x: fix CONFIG_NR_DRAM_BANKS to 1

configs: am62x: fix CONFIG_NR_DRAM_BANKS to 1

CONFIG_NR_DRAM_BANKS defines the number of DRAM banks on the
device. The default value of NR_DRAM_BANKS for ARCH_K3 is set to 2
(arch/arm/mach-k3/Kconfig:199) but should be 1 for am62x platforms.

This patch updates NR_DRAM_BANKS value for all am62x platforms to 1.

Fixes: 2969ed31b893 ("configs: Add am62x_beagleplay_*_defconfig")
Fixes: 2d257d9279e3 ("configs: Add configs for AM62x SK")
Fixes: 085cd6459dae ("board: phytec: am62x: Add PHYTEC phyCORE-AM62x SoM")
Fixes: 7d1a10659f5b ("board: toradex: add verdin am62 support")
Signed-off-by: Anshul Dalal <anshuld@ti.com>