qemu-options: Rename variables on the -numa "cpus" option

Use @var{firstcpu} and @var{lastcpu} to make the metasyntatic
variables a bit clearer. While doing this, use @var only around
the metasyntatic variables, not including the square brackets and
hyphen.

The semantics of the "cpus" option will be clarified by rewriting
the whole -numa documentation in a follow-up patch.
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170123180632.28942-2-ehabkost@redhat.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

qemu-options.hx

@@ -119,11 +119,11 @@ specifies the maximum number of hotpluggable CPUs.
 ETEXI
 
 DEF("numa", HAS_ARG, QEMU_OPTION_numa,
-    "-numa node[,mem=size][,cpus=cpu[-cpu]][,nodeid=node]\n"
-    "-numa node[,memdev=id][,cpus=cpu[-cpu]][,nodeid=node]\n", QEMU_ARCH_ALL)
+    "-numa node[,mem=size][,cpus=firstcpu[-lastcpu]][,nodeid=node]\n"
+    "-numa node[,memdev=id][,cpus=firstcpu[-lastcpu]][,nodeid=node]\n", QEMU_ARCH_ALL)
 STEXI
-@item -numa node[,mem=@var{size}][,cpus=@var{cpu[-cpu]}][,nodeid=@var{node}]
-@itemx -numa node[,memdev=@var{id}][,cpus=@var{cpu[-cpu]}][,nodeid=@var{node}]
+@item -numa node[,mem=@var{size}][,cpus=@var{firstcpu}[-@var{lastcpu}]][,nodeid=@var{node}]
+@itemx -numa node[,memdev=@var{id}][,cpus=@var{firstcpu}[-@var{lastcpu}]][,nodeid=@var{node}]
 @findex -numa
 Simulate a multi node NUMA system. If @samp{mem}, @samp{memdev}
 and @samp{cpus} are omitted, resources are split equally. Also, note