cmd: pci: Adjust display of digits for 64bit address and size

The command "pci bar" and "pci region" display the address and size in
16 characters including "0x", so the command can only display
14 hexadecimal digits if the number of digits in the address and size is
less than 14.

    ID   Base                Size                Width  Type
    ----------------------------------------------------------
     0   0x00000020000000  0x00000000100000  64     MEM   Prefetchable
     1   0xffff000080000000  0x00000000100000  64     MEM   Prefetchable

The 64-bit address and size should be displayed in 18(= 16+2) digits,
so this patch adjusts them.

Cc: Yehuda Yitschak <yehuday@marvell.com>
Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>