Use ptid from regcache in almost all remaining nat files

Use ptid from regcache in almost all remaining nat files

This patch contains almost all of the remaining changes needed to make
to_fetch_registers/to_store_registers/to_prepare_to_store independent of
inferior_ptid.  It contains only some "trivial" changes, the more
complicated ones are in separate patches.

gdb/ChangeLog:

	* i386-linux-nat.c (fetch_register, store_register,
	i386_linux_fetch_inferior_registers,
	i386_linux_store_inferior_registers): Use ptid from regcache.
	* ia64-linux-nat.c (ia64_linux_fetch_register,
	ia64_linux_store_register): Likewise.
	* inf-ptrace.c (inf_ptrace_fetch_register,
	inf_ptrace_store_register): Likewise.
	* m32r-linux-nat.c (m32r_linux_fetch_inferior_registers,
	m32r_linux_store_inferior_registers): Likewise.
	* m68k-bsd-nat.c (m68kbsd_fetch_inferior_registers,
	m68kbsd_store_inferior_registers): Likewise.
	* m68k-linux-nat.c (fetch_register, store_register,
	m68k_linux_fetch_inferior_registers,
	m68k_linux_store_inferior_registers): Likewise.
	* m88k-bsd-nat.c (m88kbsd_fetch_inferior_registers,
	m88kbsd_store_inferior_registers): Likewise.
	* mips-fbsd-nat.c (mips_fbsd_fetch_inferior_registers,
	mips_fbsd_store_inferior_registers): Likewise.
	* mips-linux-nat.c (mips64_linux_regsets_fetch_registers,
	mips64_linux_regsets_store_registers): Likewise.
	* mips-nbsd-nat.c (mipsnbsd_fetch_inferior_registers,
	mipsnbsd_store_inferior_registers): Likewise.
	* mips-obsd-nat.c (mips64obsd_fetch_inferior_registers,
	mips64obsd_store_inferior_registers): Likewise.
	* nto-procfs.c (procfs_fetch_registers, procfs_store_registers):
	Likewise.
	* ppc-fbsd-nat.c (ppcfbsd_fetch_inferior_registers,
	ppcfbsd_store_inferior_registers): Likewise.
	* ppc-linux-nat.c (ppc_linux_fetch_inferior_registers,
	ppc_linux_store_inferior_registers): Likewise.
	* ppc-nbsd-nat.c (ppcnbsd_fetch_inferior_registers,
	ppcnbsd_store_inferior_registers): Likewise.
	* ppc-obsd-nat.c (ppcobsd_fetch_registers,
	ppcobsd_store_registers): Likewise.
	* procfs.c (procfs_fetch_registers, procfs_store_registers):
	Likewise.
	* ravenscar-thread.c (ravenscar_fetch_registers,
	ravenscar_store_registers, ravenscar_prepare_to_store):
	Likewise.
	* record-btrace.c (record_btrace_fetch_registers,
	record_btrace_store_registers, record_btrace_prepare_to_store):
	Likewise.
	* remote-sim.c (gdbsim_fetch_register, gdbsim_store_register):
	Lookup inferior using ptid from regcache, instead of
	current_inferior.
	* remote.c (remote_fetch_registers, remote_store_registers): Use
	ptid from regcache.
	* rs6000-nat.c (fetch_register, store_register): Likewise.
	* s390-linux-nat.c (s390_linux_fetch_inferior_registers,
	s390_linux_store_inferior_registers): Likewise.
	* sh-nbsd-nat.c (shnbsd_fetch_inferior_registers,
	shnbsd_store_inferior_registers): Likewise.
	* sol-thread.c (sol_thread_fetch_registers,
	sol_thread_store_registers): Likewise.
	* sparc-nat.c (sparc_fetch_inferior_registers,
	sparc_store_inferior_registers): Likewise.
	* tilegx-linux-nat.c (fetch_inferior_registers,
	store_inferior_registers): Likewise.
	* vax-bsd-nat.c (vaxbsd_fetch_inferior_registers,
	vaxbsd_store_inferior_registers): Likewise.
	* xtensa-linux-nat.c (fetch_gregs, store_gregs, fetch_xtregs,
	store_xtregs): Likewise.