[elf][non-regset] uninline elf_core_copy_task_fpregs() (and lose pt_regs argument)

Don't bother with pointless macros - we are not sharing it with aout coredumps
anymore.  Just convert the underlying functions to the same arguments (nobody
uses regs, actually) and call them elf_core_copy_task_fpregs().  And unexport
the entire bunch, while we are at it.

[added missing includes in arch/{csky,m68k,um}/kernel/process.c to avoid extra
warnings about the lack of externs getting added to huge piles for those
files.  Pointless, but...]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>