drm/omap: fix crash if there's no video PLL

drm/omap: fix crash if there's no video PLL

Commit 8a7eda7686675b73d74c22c0d5b83059f9d783f6 ("drm: omapdrm: dispc:
Pass DISPC pointer to remaining dispc API functions") made dpi.c use
ctx->pll even when there's no PLL, causing a crash at modeset on AM4
EVM, and presumably all OMAP2/3 boards.

Fix this by having struct dpi_data pointer in the ctx instead, giving
access to dispc without going through the pll.

Fixes: 8a7eda768667 ("drm: omapdrm: dispc: Pass DISPC pointer to remaining dispc API functions")
Signed-off-by: Tomi Valkeinen <[email protected]>
Reported-by: Keerthy <[email protected]>
Cc: Laurent Pinchart <[email protected]>
Tested-by: Keerthy <[email protected]>
Reviewed-by: Laurent Pinchart <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]