misc: Change cpu ID type from u8 to u32

This is the first change to Cloud Hypervisor in a series of changes
intended to increase the max number of supported vCPUs in guest VMs,
which is currently limited to 255 (254 on x86_64).

No user-visible/behavior changes are expected as a result of
applying this patch, as the type of boot_cpus and related
fields in config structs remains u8 for now, and all configuration
validations remain the same.

Signed-off-by: Barret Rhoden <brho@google.com>
Signed-off-by: Neel Natu <neelnatu@google.com>
Signed-off-by: Ofir Weisse <oweisse@google.com>
Signed-off-by: Peter Oskolkov <posk@google.com>

src/bin/ch-remote.rs

@@ -725,7 +725,7 @@ fn resize_config(
     memory: Option<&str>,
     balloon: Option<&str>,
 ) -> Result<String, Error> {
-    let desired_vcpus: Option<u8> = if let Some(cpus) = cpus {
+    let desired_vcpus: Option<u32> = if let Some(cpus) = cpus {
         Some(cpus.parse().map_err(Error::InvalidCpuCount)?)
     } else {
         None