misc: Support left-justification in printk()

This is supported by printf(), and is an important formatting feature
to print out some complex, nicely-formatted information.  This is
accomplished by using a negative padding in the formatting string.

The following code:

      printk("none:         |%u| |%x|\n", 12345, 12345);
      printk("zero_before:  |%08u| |%08x|\n", 12345, 12345);
      printk("space_before: |%8u| |%8x|\n", 12345, 12345);
      printk("space_after:  |%-8u| |%-8x|\n", 12345, 12345);

Will produce the following output:

      none:         |12345| |3039|
      zero_before:  |00012345| |0000000000003039|
      space_before: |   12345| |            3039|
      space_after:  |12345   | |3039            |

Change-Id: I9c2d85a1790087d53b52b7713854adaf99282f09
Jira: ZEP-1599
Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>