lib: utils: reset: Add T-HEAD sample platform reset driver

This driver is for T-HEAD test chip, fpga. It could work with
all T-HEAD riscv processors: C9xx series.

example1: (Using io-regs for reset)
reset: reset-sample {
	compatible = "thead,reset-sample";
	plic-delegate = <0xff 0xd81ffffc>;
	entry-reg = <0xff 0xff019050>;
	entry-cnt = <4>;
	control-reg = <0xff 0xff015004>;
	control-val = <0x1c>;
	csr-copy = <0x7f3 0x7c0 0x7c1 0x7c2 0x7c3 0x7c5 0x7cc>;
};

example2: (Using csr-regs for reset)
reset: reset-sample {
	compatible = "thead,reset-sample";
	plic-delegate = <0xff 0xd81ffffc>;
	using-csr-reset;
	csr-copy = <0x7c0 0x7c1 0x7c2 0x7c3 0x7c5 0x7cc
		    0x3b0 0x3b1 0x3b2 0x3b3
		    0x3b4 0x3b5 0x3b6 0x3b7
		    0x3a0>;
};

example3: (Only delegate plic enable to S-mode)
reset: reset-sample {
	compatible = "thead,reset-sample";
	plic-delegate = <0xff 0xd81ffffc>;
};

After this patch, all T-HEAD c9xx would use platform/generic with fw_dynamic
as default:

CROSS_COMPILE=riscv64-linux-gnu- PLATFORM=generic FW_PIC=y /usr/bin/make

The platform/thead will be deprecated.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>

lib/utils/reset/fdt_reset_thead_asm.S

@@ -0,0 +1,47 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <sbi/riscv_asm.h>
+#include "fdt_reset_thead.h"
+
+/*
+ * csrrs rd, csr, rs1
+ * |31   20|19   15|14   12|11  7|6       0|
+ *    csr     rs1     010     rd   1110011
+ */
+#define CSR_STUB	addi    x0, x0, 0
+
+	.option norvc
+	.align 3
+	.global __fdt_reset_thead_csrr
+__fdt_reset_thead_csrr:
+	csrrs a0, 0, x0
+	ret
+
+	.align 3
+	.global __thead_pre_start_warm
+__thead_pre_start_warm:
+	/*
+	 * Clear L1 cache & BTB & BHT ...
+	 */
+	li	t1, 0x70013
+	csrw	0x7c2, t1
+	fence rw,rw
+
+	lla	t1, custom_csr
+
+	.global __reset_thead_csr_stub
+__reset_thead_csr_stub:
+.rept	MAX_CUSTOM_CSR
+	REG_L	t2, 8(t1)
+	CSR_STUB
+	addi	t1, t1, 16
+.endr
+	/*
+	 * Clear L1 cache & BTB & BHT ...
+	 */
+	li	t1, 0x70013
+	csrw	0x7c2, t1
+	fence rw,rw
+	j _start_warm