x86/fault: Clean up the page fault oops decoder a bit

x86/fault: Clean up the page fault oops decoder a bit

 - Make the oops messages a bit less scary (don't mention 'HW errors')

 - Turn 'PROT USER' (which is visually easily confused with PROT_USER)
   into individual bit descriptors: "[PROT] [USER]".
   This also makes "[normal kernel read fault]" more apparent.

 - De-abbreviate variables to make the code easier to read

 - Use vertical alignment where appropriate.

 - Add comment about string size limits and the helper function.

 - Remove unnecessary line breaks.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>