drm/msm/dpu: change _dpu_plane_calc_bw() to use u64 to avoid overflow

_dpu_plane_calc_bw() uses integer variables to calculate the bandwidth
used during plane bandwidth calculations. However for high resolution
displays this overflows easily and leads to below errors

[dpu error]crtc83 failed performance check -7

Promote the intermediate variables to u64 to avoid overflow.

changes in v2:
- change to u64 where actually needed in the math

Fixes: c33b7c0389e1 ("drm/msm/dpu: add support for clk and bw scaling for display")
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Reported-by: Nia Espera <[e-mail]>
Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/32
Tested-by: Nia Espera <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/556288/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Abhinav Kumar <[e-mail]>

drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c

···
 	struct dpu_sw_pipe_cfg *pipe_cfg)
 {
 	int src_width, src_height, dst_height, fps;
+	u64 plane_pixel_rate, plane_bit_rate;
 	u64 plane_prefill_bw;
 	u64 plane_bw;
 	u32 hw_latency_lines;
···
 	scale_factor = src_height > dst_height ?
 		mult_frac(src_height, 1, dst_height) : 1;
 
-	plane_bw =
-		src_width * mode->vtotal * fps * fmt->bpp *
-		scale_factor;
+	plane_pixel_rate = src_width * mode->vtotal * fps;
+	plane_bit_rate = plane_pixel_rate * fmt->bpp;
 
-	plane_prefill_bw =
-		src_width * hw_latency_lines * fps * fmt->bpp *
-		scale_factor * mode->vtotal;
+	plane_bw = plane_bit_rate * scale_factor;
+
+	plane_prefill_bw = plane_bw * hw_latency_lines;
 
 	if ((vbp+vpw) > hw_latency_lines)
 		do_div(plane_prefill_bw, (vbp+vpw));