um: PTRACE_[GS]ETFPXREGS had been wired on the wrong subarch

It's 32bit-only, not 64bit-only...  And while we are at it, it's
set_fpxregs(), not set_fpregs()...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>