drm/amd/display: Add delay in dmub_srv_send_gpint_command

[Why]
Today a parameter is passed to dmub_srv_send_gpint_command
which specifies the max amount of time to wait for the command
to be acked.
This parameter instead specifies the number of times to check if
the command was acked.
We wish to add a lower bound to the timeout, which can be
accomplished by using a delay or a timestamp.
It has been decided to use udelay instead of a timestamp simply
because we don't want to expose a high precision counter if it
doesn't yield large benefits.

[How]
Add udelay(1) between each for loop iteration.
Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dmub/src/dmub_srv.c

@@ -647,6 +647,8 @@ dmub_srv_send_gpint_command(struct dmub_srv *dmub,
 	dmub->hw_funcs.set_gpint(dmub, reg);
 
 	for (i = 0; i < timeout_us; ++i) {
+		udelay(1);
+
 		if (dmub->hw_funcs.is_gpint_acked(dmub, reg))
 			return DMUB_STATUS_OK;
 	}