perf/x86/intel: Constify the 'lbr_desc[]' array and make a function static

perf/x86/intel: Constify the 'lbr_desc[]' array and make a function static

A few minor clean-ups: constify the lbr_desc[] array and make
local function lbr_from_signext_quirk_rd() static to fix a sparse warning:

  "symbol 'lbr_from_signext_quirk_rd' was not declared. Should it be static?"

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-janitors@vger.kernel.org
Link: http://lkml.kernel.org/r/20170629091406.9870-1-colin.king@canonical.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>