remoteproc/wkup_m3: Use reset control driver if available

In order to move wkup_m3 to probe without platform data, let's add
support for using optional reset control driver if configured in the
dts. With this change and the related dts change, we can start
dropping the platform data for am335x.

And once wkup_m3 no longer needs platform data, we can simply drop the
related legacy reset platform data callbacks from wkup_m3 driver later
on after also am437x no longer depends on it.

Cc: linux-remoteproc@vger.kernel.org
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Dave Gerlach <d-gerlach@ti.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>