display_options:print_buffer: align ASCII print

display_options:print_buffer: align ASCII print

This patch adds whitespace to the printed hex numbers to have an aligned ASCII
printout at the end of the line.

This changes for example the md output from:

---8<---
OMAP3 Tricorder # md.l $loadaddr 5
82000000: 30200109 20a4028c 90010000 08a00000    .. 0... ........
82000010: 01010000    ....
--->8---

to

---8<---
OMAP3 Tricorder # md.l $loadaddr 5
82000000: 30200109 20a4028c 90010000 08a00000    .. 0... ........
82000010: 01010000                               ....
--->8---

The cost of this is about 72 byte .text increase (tested with at91 build).

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>