plat: imx8mn: change DISPMIX power domain handling

Since 'bus_blk_clk_rst' and 'bus_blk_clk_en' reset lines
are shared by each module in DISPMIX, so they are better
to be handled in power domain function of ATF. And other
reset lines are exclusively used by each module, so they
are better to be handled in Linux kernel drivers.
Signed-off-by: Fancy Fang <chen.fang@nxp.com>

plat/imx/imx8mn/gpc.c

@@ -667,9 +667,11 @@ static void imx_gpc_pm_domain_enable(uint32_t domain_id, uint32_t on)
 		}
 
 		if (domain_id == DISPMIX) {
-			/* special setting for DISPMIX */
-			/* mmio_write_32(0x32e28000, 0x7f); */
-			mmio_write_32(0x32e28004, 0x1fff);
+			/* de-reset bus_blk clk and
+			 * enable bus_blk clk
+			 */
+			mmio_write_32(0x32e28000, 0x100);
+			mmio_write_32(0x32e28004, 0x100);
 		}
 
 		/* handle the ADB400 sync */
@@ -704,6 +706,11 @@ static void imx_gpc_pm_domain_enable(uint32_t domain_id, uint32_t on)
 				;
 		}
 
+		if (domain_id == DISPMIX) {
+			mmio_write_32(0x32e28000, 0x0);
+			mmio_write_32(0x32e28004, 0x0);
+		}
+
 		/* HSIOMIX has no PU bit, so skip for it */
 		if (domain_id != HSIOMIX) {
 			/* set the PGC bit */