media: tc358743: fix connected/active CSI-2 lane reporting

g_mbus_config was supposed to indicate all supported lane numbers, not
only the number of those currently in active use. Since the TC358743
can dynamically reduce the number of active lanes if the required
bandwidth allows for it, report all lane numbers up to the connected
number of lanes as supported in pdata mode.
In device tree mode, do not report lane count and clock mode at all, as
the receiver driver can determine these from the device tree.

To allow communicating the number of currently active lanes, add a new
bitfield to the v4l2_mbus_config flags. This is a temporary fix, to be
used only until a better solution is found.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>