lib: utils: reset: thead: add back "plic-delegate" handling

When backporting commit 78c2b19218bd ("lib: utils/irqchip:
Automatically delegate T-HEAD PLIC access"), we removed the delegate
property handling as upstream does, but it will break sdk linux
kernel which still relies on "plic-delegate" property, add back
it.

lib/utils/reset/fdt_reset_thead.c

@@ -82,6 +82,13 @@ static int thead_reset_init(void *fdt, int nodeoff,
 			clone_csrs(cnt);
 	}
 
+	/* Delegate plic enable regs for S-mode */
+	val = fdt_getprop(fdt, nodeoff, "plic-delegate", &len);
+	if (len > 0 && val) {
+		p = (void *)(ulong)fdt64_to_cpu(*val);
+		writel(BIT(0), p);
+	}
+
 	/* Old reset method for secondary harts */
 	if (fdt_getprop(fdt, nodeoff, "using-csr-reset", &len)) {
 		csr_write(0x7c7, (ulong)&__thead_pre_start_warm);