x86: setup_sigcontext(): list user_access_{begin,end}() into callers

Similar to ia32_setup_sigcontext() change several commits ago, make it
__always_inline.  In cases when there is a user_access_{begin,end}()
section nearby, just move the call over there.

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