reset: oxnas: make it explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/reset/Kconfig:config RESET_OXNAS
drivers/reset/Kconfig:  bool

...meaning that it currently is not being built as a module by anyone.

Lets remove the couple traces of modular infrastructure use, so that
when reading the driver there is no doubt it is builtin-only.

Since module_platform_driver() uses the same init level priority as
builtin_platform_driver() the init ordering remains unchanged with
this commit.

Also note that MODULE_DEVICE_TABLE is a no-op for non-modular code.

Cc: linux-oxnas@lists.tuxfamily.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>