x86/boot: Fix pr_debug() API braindamage

What looked like a straightforward conversion from printk(KERN_DEBUG, ...)
to pr_debug() broke the boot log output:

  DMI:    /M57SLI-S4, BIOS FF 01/24/2008
 -e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
 -e820: remove [mem 0x000a0000-0x000fffff] usable
 +usable ==> reserved
 +usable
  e820: last_pfn = 0x230000 max_arch_pfn = 0x400000000

 ...

  x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB  WC  UC- WT
 -e820: update [mem 0xd0000000-0xffffffff] usable ==> reserved
 +usable ==> reserved

i.e. spurious (and nonsensical) kernel log entries were created...

We need a pr_debug_and_I_mean_it() function which does nothing but
printk(KERN_DEBUG...

Signed-off-by: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
[ Wrote changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>