drm/i915/dsi: Add some debug logging to mipi_exec_i2c (v2)

Add some debug logging to mipi_exec_i2c, to make debugging various
issues seen with it easier.

Changes in v2:
- Drop unnecessary __func__ drm_dbg_kms() argument

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230920195613.304091-5-hdegoede@redhat.com