drivers/power: Convert non-modular syscon-reboot to use builtin_platform_driver

This file depends on Kconfig options all of which are a bool, so
we use the appropriate registration function, which avoids us
relying on an implicit inclusion of <module.h> which we are
doing currently.

While this currently works, we really don't want to be including
the module.h header in non-modular code, which we'd be forced
to do, pending some upcoming code relocation from init.h into
module.h.  So we fix it now by using the non-modular equivalent.

Cc: Sebastian Reichel <sre@kernel.org>
Acked-By: Sebastian Reichel <sre@kernel.org>
Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: linux-pm@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>