Move some ppc macros to nat/ppc-linux.h

Move some ppc macros to nat/ppc-linux.h

When I use PPC_FEATURE_BOOKE in GDBserver, I find it is defined in GDB
but not in GDBserver.  After taking a further look, I find some macros
are duplicated between ppc-linux-nat.c and linux-ppc-low.c, so this
patch is to move them into nat/ppc-linux.h.

gdb/gdbserver:

2015-01-14  Yao Qi  <yao@codesourcery.com>

	* linux-ppc-low.c: Include "nat/ppc-linux.h".
	 (PPC_FEATURE_HAS_VSX): Move to nat/ppc-linux.h.
	(PPC_FEATURE_HAS_ALTIVEC,  PPC_FEATURE_HAS_SPE): Likewise.
	(PT_ORIG_R3, PT_TRAP): Likewise.
	(PTRACE_GETVSXREGS, PTRACE_SETVSXREGS): Likewise.
	(PTRACE_GETVRREGS, PTRACE_SETVRREGS): Likewise.
	(PTRACE_GETEVRREGS, PTRACE_SETEVRREGS): Likewise.

gdb:

2015-01-14  Yao Qi  <yao@codesourcery.com>

	* ppc-linux-nat.c (PT_ORIG_R3, PT_TRAP): Move to
	nat/ppc-linux.h.
	(PPC_FEATURE_CELL, PPC_FEATURE_BOOKE): Likewise.
	(PPC_FEATURE_HAS_DFP): Likewise.
	(PTRACE_GETVRREGS, PTRACE_SETVRREGS): Likewise.
	(PTRACE_GETVSXREGS, PTRACE_SETVSXREGS): Likewise.
	(PTRACE_GETEVRREGS, PTRACE_SETEVRREGS): Likewise.
	Include "nat/ppc-linux.h".
	* nat/ppc-linux.h: New file.
	* Makefile.in (HFILES_NO_SRCDIR): Add nat/ppc-linux.h.