generic: mips: support harts to boot from mips_warm_boot

We program reset base for harts (other than hart 0) to boot at
mips_warm_boot that jumps to _start_warm. This helps to skip some code
sequence to speed up.

Signed-off-by: Chao-ying Fu <cfu@mips.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20250723204010.9927-1-cfu@mips.com
Signed-off-by: Anup Patel <anup@brainfault.org>

platform/generic/mips/mips_warm_boot.S

@@ -0,0 +1,12 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 MIPS
+ *
+ */
+	.text
+	.align	12
+	.globl	mips_warm_boot
+mips_warm_boot:
+	j	_start_warm
+	.align	2