stand: refactor overlay loading a little bit

It was pointed out that manually loading a .dtb to be used rather than
relying on platform-specific method for loading .dtb will result in overlays
not being applied. This was true because overlay loading was hacked into
fdt_platform_load_dtb, rather than done in a way more independent from how
the .dtb is loaded.

Instead, push overlay loading (for now) out into an
fdt_platform_load_overlays. This method easily allows ubldr to pull in any
fdt_overlays specified in the ub env, and omits overlay-checking on
platforms where they're not tested and/or not desired (e.g. powerpc). If we
eventually stop caring about fdt_overlays from ubenv (if we ever cared),
this method should get chopped out in favor of just calling
fdt_load_dtb_overlays() directly.

Reported by:	Manuel Stühn (freebsdnewbie freenet de)

stand/efi/fdt/efi_fdt.c

@@ -52,10 +52,16 @@ fdt_platform_load_dtb(void)
 		return (1);
 	printf("Using DTB provided by EFI at %p.\n", hdr);
 
-	fdt_load_dtb_overlays(NULL);
 	return (0);
 }
 
+void
+fdt_platform_load_overlays(void)
+{
+
+	fdt_load_dtb_overlays(NULL);
+}
+
 void
 fdt_platform_fixups(void)
 {

stand/fdt/fdt_loader_cmd.c

@@ -522,6 +522,7 @@ fdt_setup_fdtp()
 		if (fdt_load_dtb(bfp->f_addr) == 0) {
 			printf("Using DTB from loaded file '%s'.\n", 
 			    bfp->f_name);
+			fdt_platform_load_overlays();
 			return (0);
 		}
 	}
@@ -531,12 +532,15 @@ fdt_setup_fdtp()
 		if (fdt_load_dtb_addr(fdt_to_load) == 0) {
 			printf("Using DTB from memory address %p.\n",
 			    fdt_to_load);
+			fdt_platform_load_overlays();
 			return (0);
 		}
 	}
 
-	if (fdt_platform_load_dtb() == 0)
+	if (fdt_platform_load_dtb() == 0) {
+		fdt_platform_load_overlays();
 		return (0);
+	}
 
 	/* If there is a dtb compiled into the kernel, use it. */
 	if ((va = fdt_find_static_dtb()) != 0) {

stand/fdt/fdt_platform.h

@@ -51,6 +51,7 @@ int fdt_setup_fdtp(void);
 
 /* The platform library needs to implement these functions */
 int fdt_platform_load_dtb(void);
+void fdt_platform_load_overlays(void);
 void fdt_platform_fixups(void);
 
 #endif /* FDT_PLATFORM_H */

stand/powerpc/kboot/kbootfdt.c

@@ -176,6 +176,12 @@ fdt_platform_load_dtb(void)
 	return (0);
 }
 
+void
+fdt_platform_load_overlays(void)
+{
+
+}
+
 void
 fdt_platform_fixups(void)
 {

stand/powerpc/ofw/ofwfdt.c

@@ -197,6 +197,12 @@ fdt_platform_load_dtb(void)
         return (0);
 }
 
+void
+fdt_platform_load_overlays(void)
+{
+
+}
+
 void
 fdt_platform_fixups(void)
 {

stand/uboot/fdt/uboot_fdt.c

@@ -103,11 +103,16 @@ fdt_platform_load_dtb(void)
 	}
 
 exit:
-	if (rv == 0)
-		fdt_load_dtb_overlays(ub_env_get("fdt_overlays"));
 	return (rv);
 }
 
+void
+fdt_platform_load_overlays(void)
+{
+
+	fdt_load_dtb_overlays(ub_env_get("fdt_overlays"));
+}
+
 void
 fdt_platform_fixups(void)
 {