cmake: expand DTC version regex

DTC can be built with both traditional Makefiles or Meson. When built
with Makefiles the --version output looks like 'Version: DTC
1.6.1-dirty' but when built with Meson the output is 'Version: DTC
v1.6.1+.

This fails to match the version regex and the cmake then fails:

CMake Error at cmake/host-tools.cmake:28 (if):
  if given arguments:
    "VERSION_GREATER" "1.4.6"
  Unknown arguments specified

Expanding the regex with an optional 'v' covers both cases and the build
succeeds.

Signed-off-by: Ross Burton <[email protected]>

Author: rossburton

cmake/host-tools.cmake

@@ -20,7 +20,7 @@ if(DTC)
     )
 
   if(${dtc_status} EQUAL 0)
-    string(REGEX MATCH "Version: DTC ([0-9]+[.][0-9]+[.][0-9]+).*" out_var ${dtc_version_output})
+    string(REGEX MATCH "Version: DTC v?([0-9]+[.][0-9]+[.][0-9]+).*" out_var ${dtc_version_output})
 
     # Since it is optional, an outdated version is not an error. If an
     # outdated version is discovered, print a warning and proceed as if