iio: gyro: mpu3050: Use pm_ptr() and DEFINE_RUNTIME_DEV_PM_OPS()

Using this approach as opposed to CONFIG_PM guards allows the compiler to
remove the unused code instead of doing it manually.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220220175149.503495-3-jic23@kernel.org