iopoll: Introduce read_poll_timeout_atomic macro

Like read_poll_timeout, an atomic variant for multiple parameter read
function can be useful.

Will be used by a later patch.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200424184918.30360-1-kai.heng.feng@canonical.com