Update spelling "mbed TLS" to "Mbed TLS"

The official spelling of the trade mark changed from all-lowercase "mbed"
to normal proper noun capitalization "Mbed" a few years ago. We've been
using the new spelling in new text but still have the old spelling in a
lot of text. This commit updates most occurrences of "mbed TLS":

```
sed -i -e 's/mbed TLS/Mbed TLS/g' $(git ls-files ':!ChangeLog' ':!tests/data_files/**' ':!tests/suites/*.data' ':!programs/x509/*' ':!configs/tfm*')
```

Justification for the omissions:

* `ChangeLog`: historical text.
* `test/data_files/**`, `tests/suites/*.data`, `programs/x509/*`: many
  occurrences are significant names in certificates and such. Changing
  the spelling would invalidate many signatures and tests.
* `configs/tfm*`: this is an imported file. We'll follow the upstream
  updates.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/scripts/bump_version.sh b/scripts/bump_version.sh
index 57ade94..b84308d 100755
--- a/scripts/bump_version.sh
+++ b/scripts/bump_version.sh
@@ -125,7 +125,7 @@
     sed -e "s/_VERSION_PATCH .\{1,\}/_VERSION_PATCH  $PATCH/" |    \
     sed -e "s/_VERSION_NUMBER .\{1,\}/_VERSION_NUMBER         $VERSION_NR/" |    \
     sed -e "s/_VERSION_STRING .\{1,\}/_VERSION_STRING         \"$VERSION\"/" |    \
-    sed -e "s/_VERSION_STRING_FULL .\{1,\}/_VERSION_STRING_FULL    \"mbed TLS $VERSION\"/" \
+    sed -e "s/_VERSION_STRING_FULL .\{1,\}/_VERSION_STRING_FULL    \"Mbed TLS $VERSION\"/" \
     > tmp
 mv tmp include/mbedtls/version.h