pci: pci-uclass: Remove #ifdef CONFIG_NR_DRAM_BANKS as its always set

Since the migration to Kconfig, CONFIG_NR_DRAM_BANKS is configured for
all boards. Hence we can remove the conditional compilation and the code
path that will never get compiled.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Bin Meng <bmeng.cn@gmail.com>