docs: i386: pc: Update maximum CPU numbers for PC Q35

Commit e4e98c7eebfa ("pc: q35: Bump max_cpus to 4096 vcpus") increases
the supported CPUs for PC Q35 machine.

Update maximum CPU numbers for PC Q35 in the document.

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Message-ID: <20240412085358.731560-1-zhao1.liu@linux.intel.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
1 file changed