cpufreqd: Use new sys:msr scheme for P-state control

Replace non-existent /dev/cpu/{n}/msr path with /scheme/sys/msr/{cpu}/{msr}
now that the kernel exposes MSR access via the sys scheme.

local/recipes/system/cpufreqd/source/src/main.rs

@@ -58,8 +58,12 @@ fn read_acpi_pss(cpu: u32) -> Vec<PState> {
 }
 
 fn write_msr(cpu: u32, msr: u32, val: u64) -> bool {
-    fs::OpenOptions::new().write(true).open(format!("/dev/cpu/{}/msr", cpu)).ok()
-        .map(|mut f| f.write_all(&val.to_ne_bytes()).is_ok()).unwrap_or(false)
+    let path = format!("/scheme/sys/msr/{}/{:x}", cpu, msr);
+    fs::OpenOptions::new().write(true).open(&path).ok()
+        .and_then(|mut f| {
+            let hex_val = format!("{:016x}", val);
+            f.write_all(hex_val.as_bytes()).ok()
+        }).is_some()
 }
 
 fn measure_load(cpu: u32, prev: &mut (u64, u64)) -> f64 {