clocksource/timer-riscv: Add ACPI support

Initialize the timer driver based on RHCT table on ACPI based
platforms.

Currently, ACPI doesn't support a flag to indicate that the
timer interrupt can wake up the cpu irrespective of its
power state. It will be added in future update.
Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230515054928.2079268-19-sunilvl@ventanamicro.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

drivers/clocksource/timer-riscv.c

@@ -10,6 +10,7 @@
 
 #define pr_fmt(fmt) "riscv-timer: " fmt
 
+#include <linux/acpi.h>
 #include <linux/clocksource.h>
 #include <linux/clockchips.h>
 #include <linux/cpu.h>
@@ -207,3 +208,13 @@ static int __init riscv_timer_init_dt(struct device_node *n)
 }
 
 TIMER_OF_DECLARE(riscv_timer, "riscv", riscv_timer_init_dt);
+
+#ifdef CONFIG_ACPI
+static int __init riscv_timer_acpi_init(struct acpi_table_header *table)
+{
+	return riscv_timer_init_common();
+}
+
+TIMER_ACPI_DECLARE(aclint_mtimer, ACPI_SIG_RHCT, riscv_timer_acpi_init);
+
+#endif