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

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>