SG2042: add virtual global timer device driver

Add a virtual global timer device driver. It uses a global timer
register as timer counter, and it uses mtimecmp CSR of clint as
interrupt source.
Using this virtul timer resolves dual way timer sync issue.
On dual way system, we should enable this driver and on single way
system, we should use standard risc-v clint timer.

1. Add a virtual global timer device driver, it is probed by fdt

	sg2042-global-mtimer@70300101c0 {
		compatible = "sophgo,sg2042-global-mtimer";
		reg = < 0x00000070 0x300101c0 0x00000000 0x00000008
			0x00000070 0xac000000 0x00000000 0x00200000>;
		clock-frequency = <50000000 50000000>;
	};

Its compatible should be "sophgo,sg2042-global-mtimer".
And the first region delcared in reg prop is the address of global
timer. The second region delcared in reg prop is the base of clint
timers.
The first clock in clock-frequency is the actual frequency of global
timer, the second clock is the actual frequency of clint timer.

2. Add a quirk in platform specific code.
Add a function sbi_platform_force_emulate_time_csr, it indicates if
opensbi should skip time CSR detection and make software in
supervisor and user mode use emulated time CSR.

Signed-off-by: Chao Wei <chao.wei@sophgo.com>

include/sbi/riscv_encoding.h

@@ -223,6 +223,8 @@
 #define ENVCFG_CBIE_INV			_UL(0x3)
 #define ENVCFG_FIOM			_UL(0x1)
 
+#define MCOUNTEREN_TM			(_UL(1) << 1)
+
 /* ===== User-level CSRs ===== */
 
 /* User Trap Setup (N-extension) */

include/sbi/sbi_platform.h

@@ -68,6 +68,9 @@ struct sbi_platform_operations {
 	/* Check if specified HART is allowed to do cold boot */
 	bool (*cold_boot_allowed)(u32 hartid);
 
+	/* Check if platform force emulate time csr, instead of using csr directly */
+	bool (*force_emulate_time_csr)(void);
+
 	/* Platform nascent initialization */
 	int (*nascent_init)(void);
 
@@ -376,6 +379,20 @@ static inline bool sbi_platform_cold_boot_allowed(
 	return true;
 }
 
+/**
+ * Check whether given platform should force emulate time CSR
+ *
+ * @param plat pointer to struct sbi_platform
+ *
+ * @return true such platform force emulate time CSR, false otherwise
+ */
+static inline bool sbi_platform_force_emulate_time_csr(const struct sbi_platform *plat)
+{
+	if (plat && sbi_platform_ops(plat)->force_emulate_time_csr)
+		return sbi_platform_ops(plat)->force_emulate_time_csr();
+	return false;
+}
+
 /**
  * Nascent (very early) initialization for current HART
  *

include/sbi_utils/timer/sg2042_gmt.h

@@ -0,0 +1,21 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 SOPHGO Corporation
+ *
+ * Authors:
+ *   Chao Wei <chao.wei@sophgo.com>
+ */
+
+#ifndef __SG2042_GMT_H__
+#define __SG2042_GMT_H__
+
+int sg2042gmt_cold_timer_init(unsigned long mtimer_base,
+			      unsigned long mtimecmp_base,
+			      unsigned long mtimecmp_size,
+			      unsigned long delcared_freq,
+			      unsigned long actual_freq,
+			      unsigned long timecmp_freq);
+int sg2042gmt_warm_timer_init(void);
+
+#endif /* __SG2042_GMT_H__ */