mdss: add io_util.h to allow consumers to build

This is a snapshot of include/linux/mdss_io_util.h as of msm-3.10 commit

acdce027751d5a7488b283f0ce3111f873a5816d (Merge "defconfig: arm64: Enable
ONESHOT_SYNC for msm8994")

Signed-off-by: Josh Cartwright <joshc@codeaurora.org>