loader: Increase buffer size to accommodate longer commands

[VexedUXR]

The longest command we have is "efi-autoresizecons". That combined with the two spaces before and after the command gives us a total of 23 characters including the null-terminator.

Increasing this caused alignment issues since efi-autoresizecons is > 15 chars ("%-15s"). So I also increased that to 20 and removed the two spaces at the end since they aren't really needed.

Before:

Available commands:
  copy_staging     copy staging
  staging_slop     set staging slop
  efi-autoresizeconEFI Auto-resize Console <-- Cuts off
  gop              graphics output protocol
  uga              universal graphics adapter
  efi-seed-entropy try to get entropy from the EFI RNG
  poweroff         power off the system
  ...

After:

Available commands:
  copy_staging        copy staging
  staging_slop        set staging slop
  efi-autoresizecons  EFI Auto-resize Console
  gop                 graphics output protocol
  uga                 universal graphics adapter
  efi-seed-entropy    try to get entropy from the EFI RNG
  poweroff            power off the system
  ...

[bsdimp]

This is fine.. though it might be good to compute this dynamically ...