rtc: tegra: Turn into regular driver

rtc: tegra: Turn into regular driver

Drivers registered with module_platform_driver_probe() are considered
non-hotpluggable, which among other things means that they don't support
deferred probe. However, recent changes in how the ARM SMMU works have
required the BPMP (which is the clock provider on Tegra186 and later) be
bound to the SMMU, which in turn means that the BPMP driver can defer
probe and hence clocks become available much later than they used to.
For most other drivers this is not a problem because they already
properly support deferred probe, but rtc-tegra is the odd one out that
now fails to probe and will therefore never be registered.

Fix this by making the driver a regular driver that supports unloading
and deferred probe.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>