iopoll: import include/linux/iopoll.h from Linux 4.9

This was imported from Linux 4.9 and adjusted for U-Boot.

 - Replace the license block with SPDX
 - Drop all *_atomic variants, which make no sense for U-Boot
 - Remove the sleep_us argument, which makes no sense for U-Boot

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
1 file changed