remoteproc: move rproc_da_to_va declaration to remoteproc.h

The rproc_da_to_va() API is an exported function, so move its
declaration from the remoteproc local remoteproc_internal.h
to the public remoteproc.h file.

This will allow drivers outside of the remoteproc folder to be
able to use this API.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
[adjusted line numbers to apply]
Signed-off-by: Drew Fustini <dfustini@baylibre.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220308172515.29556-1-dfustini@baylibre.com