video: dw_mipi_dsi: update log of dphy_enable

The DSI phy can be turned on from the DSI digital interface in
the dphy_enable() function or from a dedicated DSI phy "wrapper"
in phy_ops->init() function. If the STM32MP1 case, the wrapper
is used then the dphy_enable() "warning" traces are not relevant.

This patch moves these "warning" traces to "debug" traces so
they are still available for DSI phy based on the digital
interface in debug logging mode, but not there in normal mode
for both cases.
Note: The related Linux kernel driver uses a "debug"
message too.

Signed-off-by: Yannick Fertre <yannick.fertre@foss.st.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Acked-by: Yannick Fertre <yannick.fertre@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>