drm/exynos: dsi: move DSIM_STATE_ENABLED set position

The command mode panel should draw image earlier than the display
on command execution to prevent showing garbage GRAM screen data.
So should set dsi->state as DSIM_STATE_ENABLED between calling
exynos_dsi_set_display_enable() and drm_panel_enable() to transmit
image data before executing display on command.
And moves the display on command execution routine from prepare()
to enable() in drm_panel_funcs also.

Signed-off-by: YoungJun Cho <yj44.cho@samsung.com>
Acked-by: Inki Dae <inki.dae@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>