drm/i915/dsi-pll: use generic poll_timeout_us() instead of wait_for()

Prefer generic poll helpers over i915 custom helpers.

The functional change is losing the exponentially growing sleep of
wait_for(), which used to be 10, 20, 40, ..., 640, and 1280 us.

Use an arbitrary constant 500 us sleep instead. The timeout remains at
20 ms.

Reviewed-by: Jouni Högander <[e-mail]>
Link: https://lore.kernel.org/r/476[e-mail]
Signed-off-by: Jani Nikula <[e-mail]>

drivers/gpu/drm/i915/display/vlv_dsi_pll.c

···
  *	Yogesh Mohan Marimuthu <[e-mail]>
  */
 
+#include <linux/iopoll.h>
 #include <linux/kernel.h>
 #include <linux/string_helpers.h>
 
 #include <drm/drm_print.h>
 
-#include "i915_utils.h"
 #include "intel_de.h"
 #include "intel_display_types.h"
 #include "intel_dsi.h"
···
 			const struct intel_crtc_state *config)
 {
 	struct intel_display *display = to_intel_display(encoder);
+	u32 val;
+	int ret;
 
 	drm_dbg_kms(display->drm, "\n");
 
···
 
 	vlv_cck_write(display->drm, CCK_REG_DSI_PLL_CONTROL, config->dsi_pll.ctrl);
 
-	if (wait_for(vlv_cck_read(display->drm, CCK_REG_DSI_PLL_CONTROL) &
-						DSI_PLL_LOCK, 20)) {
-
+	ret = poll_timeout_us(val = vlv_cck_read(display->drm, CCK_REG_DSI_PLL_CONTROL),
+			      val & DSI_PLL_LOCK,
+			      500, 20 * 1000, false);
+	if (ret) {
 		vlv_cck_put(display->drm);
 		drm_err(display->drm, "DSI PLL lock failed\n");
 		return;