In order to reduce the kernel Image size on multi-platform distributions,
make it possible to build the reset controller driver as a module.

This partially reverts commit 8290924e ("reset: meson: make it
explicitly non-modular").
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>
Reviewed-by: NKevin Hilman <khilman@baylibre.com>
Tested-by: NKevin Hilman <khilman@baylibre.com>
Reviewed-by: NMartin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: NPhilipp Zabel <p.zabel@pengutronix.de>