remoteproc: convert to DEFINE_SHOW_ATTRIBUTE

Use DEFINE_SHOW_ATTRIBUTE macro to simplify the code.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Link: https://lore.kernel.org/r/20181201155838.8619-1-tiny.windzz@gmail.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>