meson: allow building from shallow clones

When building from shallow clone, tag is not available
and version defaults to git hash.
Problem is that some builds check DTC version and fail the comparison.
Example is https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git
Which fails to build with following error:
dtc version too old (039a994), you need at least version 1.4.4

Drop --always from git describe command, see
https://github.com/mesonbuild/meson/blob/1.3.0/mesonbuild/utils/universal.py#L773
This will make it more closer to build via Makefile.

Signed-off-by: Peter Marko <peter.marko@siemens.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

meson.build

@@ -59,6 +59,7 @@ py = py.find_installation(required: get_option('python'))
 swig = find_program('swig', required: get_option('python'))
 
 version_gen_h = vcs_tag(
+  command: ['git', 'describe', '--dirty=+'],
   input: 'version_gen.h.in',
   output: 'version_gen.h',
 )