drm/i915/dsi: Drop bogus MIPI_SEQ_ASSERT_RESET before POWER_ON

intel_dsi_post_disable(), which does the MIPI_SEQ_ASSERT_RESET,
will always be called at some point before intel_dsi_pre_enable()
making the MIPI_SEQ_ASSERT_RESET in intel_dsi_pre_enable() redundant.

In addition, calling MIPI_SEQ_ASSERT_RESET in the enable path goes
against the VBT spec.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Bob Paauwe <bob.j.paauwe@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1488374106-4949-3-git-send-email-jani.nikula@intel.com