[sw] Centralize the definition of $OT_VERSION

$OT_VERSION is now defined in util/build_consts.sh. Meson, chip_info.h,
and make_distribution.sh all use this definition now.

This definition is also not dependent on git: if run outside of the git
repository, it will simply be "opentitan-<unknown>".

Fixes #1057.

Signed-off-by: Miguel Young de la Sota <mcyoung@google.com>
diff --git a/meson.build b/meson.build
index d1d1b6d..38b1483 100644
--- a/meson.build
+++ b/meson.build
@@ -9,6 +9,11 @@
   error('target option not set. Please run meson with a valid build target option.')
 endif
 
+ot_version = get_option('ot_version')
+if ot_version == 'undef'
+  error('ot_version option not set. Please run meson with a valid OpenTitan version option.')
+endif
+
 if target == 'sim-verilator'
   # TODO: Consider using extra args array if using this flag globally is no
   # longer OK.