x86: replace NT_PRXFPREG with ELF_CORE_XFPREG_TYPE #define

Replace NT_PRXFPREG with ELF_CORE_XFPREG_TYPE in the coredump code which
allows for more flexibility in the note type for the state of 'extended
floating point' implementations in coredumps.  New note types can now be
added with an appropriate #define.

This does #define ELF_CORE_XFPREG_TYPE to be NT_PRXFPREG in all
current users so there's are no change in behaviour.

This will let us use different note types on powerpc for the Altivec/VMX
state that some PowerPC cpus have (G4, PPC970, POWER6) and for the SPE
(signal processing extension) state that some embedded PowerPC cpus from
Freescale have.

Signed-off-by: Mark Nelson <markn@au1.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Andi Kleen <ak@suse.de>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>