remoteproc: Add kernel-doc comment for is_iomem

Add a kernel-doc comment for the is_iomem function argument in
rproc_da_to_va(). This fixes a warning generated when building
the remoteproc_core with W=1,
  warning: Function parameter or member 'is_iomem' not described in 'rproc_da_to_va'

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suman Anna <s-anna@ti.com>
Link: https://lore.kernel.org/r/20210519180304.23563-2-s-anna@ti.com


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