x86/cpufeatures: Fix various details in the feature definitions

Kept this commit separate from the re-tabulation changes, to make
the changes easier to review:

 - add better explanation for entries with no explanation
 - fix/enhance the text of some of the entries
 - fix the vertical alignment of some of the feature number definitions
 - fix inconsistent capitalization
 - ... and lots of other small details

i.e. make it all more of a coherent unit, instead of a patchwork of years of additions.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171031121723.28524-4-mingo@kernel.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>