x86/fpu: Clarify parameter names in the copy_xstate_to_*() methods

x86/fpu: Clarify parameter names in the copy_xstate_to_*() methods

Right now there's a confusing mixture of 'offset' and 'size' parameters:

 - __copy_xstate_to_*() input parameter 'end_pos' not not really an offset,
   but the full size of the copy to be performed.

 - input parameter 'count' to copy_xstate_to_*() shadows that of
   __copy_xstate_to_*()'s 'count' parameter name - but the roles
   are different: the first one is the total number of bytes to
   be copied, while the second one is a partial copy size.

To unconfuse all this, use a consistent set of parameter names:

 - 'size' is the partial copy size within a single xstate component
 - 'size_total' is the total copy requested
 - 'offset_start' is the requested starting offset.
 - 'offset' is the offset within an xstate component.

No change in functionality.

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: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/20170923130016.21448-9-mingo@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>