x86: Constify attribute_group structures

attribute_groups are not supposed to change at runtime and none of the
groups is modified.

Mark the non-const structs as const.

[ tglx: Folded into one big patch ]

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: tony.luck@intel.com
Cc: bp@alien8.de
Link: http://lkml.kernel.org/r/1500550238-15655-2-git-send-email-arvind.yadav.cs@gmail.com