docs: update CPU option examples

Use the structured --cpus boot= syntax in cloud-hypervisor launch
examples so they match the current VM config parser.

On-behalf-of: SAP philipp.schuster@sap.com
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>

docs/debug-port.md

@@ -54,7 +54,7 @@ to easily grep for the tracing logs (e.g.
 ./target/debug/cloud-hypervisor \
     --kernel ~/rust-hypervisor-firmware/target/release/hypervisor-fw \
     --disk path=~/hypervisor/images/focal-server-cloudimg-amd64.raw \
-    --cpus 4 \
+    --cpus boot=4 \
     --memory size=1024M \
     --rng \
     --log-file /tmp/ch-fw.log \

docs/vfio.md

@@ -85,7 +85,7 @@ takes the device's sysfs path as an argument. In our example it is
     --console off \
     --serial tty \
     --cmdline "console=ttyS0 root=/dev/vda1 rw" \
-    --cpus 4 \
+    --cpus boot=4 \
     --memory size=512M \
     --device path=/sys/bus/pci/devices/0000:01:00.0/
 ```