remoteproc/davinci: fix unbalanced reset between start and stop ops

The davinci remoteproc driver is currently de-asserting the reset in
its rproc .start() ops, but is not asserting the reset in its .stop()
ops. This leaves the remote processor to not boot properly when using
the sysfs 'state' variable between multiple start and stop operations.
On the other hand, a reset is being asserted unconditionally in the
driver remove function to alleviate some of these issues.

Move this reset assertion logic into the .stop() ops implementation
to fix the sysfs state-machine and the unbalanced reset. The logic
from remove is still effective since .stop() ops will be invoked
during the remove due to the enabled 'auto-boot' support. The probe
already has support for asserting the reset in case the DSP is not
in reset for some reason.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>