fork: move the real prepare_to_copy() users to arch_dup_task_struct()

fork: move the real prepare_to_copy() users to arch_dup_task_struct()

Historical prepare_to_copy() is mostly a no-op, duplicated for majority of
the architectures and the rest following the x86 model of flushing the extended
register state like fpu there.

Remove it and use the arch_dup_task_struct() instead.

Suggested-by: Oleg Nesterov <[email protected]>
Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Suresh Siddha <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Acked-by: Benjamin Herrenschmidt <[email protected]>
Cc: David Howells <[email protected]>
Cc: Koichi Yasutake <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Paul Mundt <[email protected]>
Cc: Chris Zankel <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Russell King <[email protected]>
Cc: Haavard Skinnemoen <[email protected]>
Cc: Mike Frysinger <[email protected]>
Cc: Mark Salter <[email protected]>
Cc: Aurelien Jacquiot <[email protected]>
Cc: Mikael Starvik <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Cc: Richard Kuo <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Michal Simek <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Jonas Bonn <[email protected]>
Cc: James E.J. Bottomley <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Chen Liqin <[email protected]>
Cc: Lennox Wu <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Jeff Dike <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Guan Xuetao <[email protected]>
Signed-off-by: H. Peter Anvin <[email protected]>