unix: add riscv_hwprobe for riscv64

The riscv_hwprobe system call was introduced in Linux 6.4 and allows
the caller to determine a number of interesting pieces of information
about the underlying RISC-V CPUs, e.g., which extensions they support
and whether they allow fast unaligned memory accesses.  For more information
please see:

https://docs.kernel.org/riscv/hwprobe.html

We also update linux/mksysnum.go to ensure that the generated syscall constants
written to the zsysnum_linux_*.go files are always sorted by their syscall numbers
in ascending order.

Updates golang/go#61416

Change-Id: Iedb0a86adb65faac9061b9a5969ffa09eb5b303a
Reviewed-on: https://go-review.googlesource.com/c/sys/+/510795
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>

unix/zsyscall_linux_riscv64.go

@@ -531,3 +531,19 @@ func kexecFileLoad(kernelFd int, initrdFd int, cmdlineLen int, cmdline string, f
 	}
 	return
 }
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
+func riscvHWProbe(pairs []RISCVHWProbePairs, cpuCount uintptr, cpus *CPUSet, flags uint) (err error) {
+	var _p0 unsafe.Pointer
+	if len(pairs) > 0 {
+		_p0 = unsafe.Pointer(&pairs[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
+	}
+	_, _, e1 := Syscall6(SYS_RISCV_HWPROBE, uintptr(_p0), uintptr(len(pairs)), uintptr(cpuCount), uintptr(unsafe.Pointer(cpus)), uintptr(flags), 0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}