phy: rcar: Split init and set_mode operations

phy: rcar: Split init and set_mode operations

The current init operation also sets the PHY into USB host mode.
Split the mode configuration into set_mode callback instead and
implement support for device and OTG modes as well.

The OTG mode performs auto-detection and selects either host or
device mode. In case the OTG mode is configured, submode field
can be used to select full PHY (re)initialization or only mode
auto-detection. The full (re)initialization is only necessary
once, on start up.

Since the OTG mode may enable IRQ generation in the PHY, disable
that IRQ generation in the exit callback again.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>