Qemu has deprecated extension name with capital 'Z'

See this for detail:
https://www.qemu.org/docs/master/about/deprecated.html#risc-v-cpu-properties-which-start-with-capital-z-since-8-2

Author: kito-cheng

scripts/march-to-cpu-opt

@@ -13,10 +13,10 @@ QEMU_EXT_OPTS = {
   "zbc":             "zbc=true",
   "zbs":             "zbs=true",
   "v":               "v=true,vext_spec=v1.0",
-  "zve32f":          "Zve32f=true",
-  "zve64f":          "Zve64f=true",
-  "zfh":             "Zfh=true",
-  "zfhmin":          "Zfhmin=true",
+  "zve32f":          "zve32f=true",
+  "zve64f":          "zve64f=true",
+  "zfh":             "zfh=true",
+  "zfhmin":          "zfhmin=true",
   "zhinx":           "zhinx=true",
   "zfinx":           "zfinx=true",
   "zdinx":           "zdinx=true",