UPSTREAM: x86/uaccess: force copy_*_user() to be inlined

As already done with __copy_*_user(), mark copy_*_user() as __always_inline.
Without this, the checks for things like __builtin_const_p() won't work
consistently in either hardened usercopy nor the recent adjustments for
detecting usercopy overflows at compile time.

The change in kernel text size is detectable, but very small:

 text      data     bss     dec      hex     filename
12118735  5768608 14229504 32116847 1ea106f vmlinux.before
12120207  5768608 14229504 32118319 1ea162f vmlinux.after

Signed-off-by: Kees Cook <keescook@chromium.org>

Change-Id: I284c85c2a782145f46655a91d4f83874c90eba61
(cherry picked from commit e6971009a95a74f28c58bbae415c40effad1226c)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>