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/tests/suites/test_suite_version.function b/tests/suites/test_suite_version.function
index 981f8ab..eeae512 100644
--- a/tests/suites/test_suite_version.function
+++ b/tests/suites/test_suite_version.function
@@ -20,7 +20,7 @@
     mbedtls_snprintf(build_str, 100, "%d.%d.%d", MBEDTLS_VERSION_MAJOR,
                      MBEDTLS_VERSION_MINOR, MBEDTLS_VERSION_PATCH);
 
-    mbedtls_snprintf(build_str_full, 100, "mbed TLS %d.%d.%d", MBEDTLS_VERSION_MAJOR,
+    mbedtls_snprintf(build_str_full, 100, "Mbed TLS %d.%d.%d", MBEDTLS_VERSION_MAJOR,
                      MBEDTLS_VERSION_MINOR, MBEDTLS_VERSION_PATCH);
 
     build_int = MBEDTLS_VERSION_MAJOR << 24 |
@@ -56,7 +56,7 @@
                      (get_int >> 24) & 0xFF,
                      (get_int >> 16) & 0xFF,
                      (get_int >> 8) & 0xFF);
-    mbedtls_snprintf(build_str_full, 100, "mbed TLS %s", version_str);
+    mbedtls_snprintf(build_str_full, 100, "Mbed TLS %s", version_str);
 
     TEST_ASSERT(strcmp(build_str, version_str) == 0);
     TEST_ASSERT(strcmp(build_str_full, get_str_full) == 0);