feat(imx8m): add the PU power domain support on imx8mm/mn

Add the PU power domain support for imx8mm/mn.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Change-Id: Ib88b4b5db956fdf2c77d2f2f3723d61a7060409d
diff --git a/plat/imx/imx8m/imx8mp/gpc.c b/plat/imx/imx8m/imx8mp/gpc.c
index 3d68b94..452e788 100644
--- a/plat/imx/imx8m/imx8mp/gpc.c
+++ b/plat/imx/imx8m/imx8mp/gpc.c
@@ -170,7 +170,7 @@
 	}
 }
 
-static void imx_gpc_pm_domain_enable(uint32_t domain_id, bool on)
+void imx_gpc_pm_domain_enable(uint32_t domain_id, bool on)
 {
 	struct imx_pwr_domain *pwr_domain = &pu_domains[domain_id];
 	unsigned int i;